Rt-thread提供的printf实现（rt_vsnprintf的实现）
前言
很多情况下需要自己实现printf,有时是即有的printf改了半天设置仍不满足要求，比如体积太大，或者是其功能不够。这里记录一个常用的自行实现的全功能printf.
这个是从rt-thread上抄来的，gcc下，是一个完整的c文件。
实现
rt_vsnprintf
/*
* Copyright (c) 2021, Meco Jianting Man <jiantingman@foxmail.com>
*
* SPDX-License-Identifier: Apache-2.0
*
* Change Logs:
* Date Author Notes
* 2021-11-27 Meco Man porting for rt_vsnprintf as the fully functional version
*/
/**
* @author (c) Eyal Rozenberg <eyalroz1@gmx.com>
* 2021, Haifa, Palestine/Israel
* @author (c) Marco Paland (info@paland.com)
* 2014-2019, PALANDesign Hannover, Germany
*
* @note Others have made smaller contributions to this file: see the
* contributors page at https://github.com/eyalroz/printf/graphs/contributors
* or ask one of the authors.
*
* @brief Small stand-alone implementation of the printf family of functions
* (`(v)printf`, `(v)s(n)printf` etc., geared towards use on embedded systems with
* a very limited resources.
*
* @note the implementations are thread-safe; re-entrant; use no functions from
* the standard library; and do not dynamically allocate any memory.
*
* @license The MIT License (MIT)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include <stdbool.h>
#include <stdint.h>
#include <stdarg.h>
#include <stddef.h>
// 'ntoa' conversion buffer size, this must be big enough to hold one converted
// numeric number including padded zeros (dynamically created on stack)
#define PRINTF_INTEGER_BUFFER_SIZE 32
// 'ftoa' conversion buffer size, this must be big enough to hold one converted
// float number including padded zeros (dynamically created on stack)
#define PRINTF_FTOA_BUFFER_SIZE 32
// Support for the decimal notation floating point conversion specifiers (%f, %F)
#define PRINTF_SUPPORT_DECIMAL_SPECIFIERS 1
// Support for the exponential notatin floating point conversion specifiers (%e, %g, %E, %G)
#define PRINTF_SUPPORT_EXPONENTIAL_SPECIFIERS 1
// Default precision for the floating point conversion specifiers (the C standard sets this at 6)
#define PRINTF_DEFAULT_FLOAT_PRECISION 6
// According to the C languages standard, printf() and related functions must be able to print any
// integral number in floating-point notation, regardless of length, when using the %f specifier -
// possibly hundreds of characters, potentially overflowing your buffers. In this implementation,
// all values beyond this threshold are switched to exponential notation.
#define PRINTF_MAX_INTEGRAL_DIGITS_FOR_DECIMAL 9
// Support for the long long integral types (with the ll, z and t length modifiers for specifiers
// %d,%i,%o,%x,%X,%u, and with the %p specifier). Note: 'L' (long double) is not supported.
#define PRINTF_SUPPORT_LONG_LONG 1
typedef unsigned long long printf_unsigned_value_t;
typedef long long printf_signed_value_t;
#define PRINTF_PREFER_DECIMAL false
#define PRINTF_PREFER_EXPONENTIAL true
///////////////////////////////////////////////////////////////////////////////
// The following will convert the number-of-digits into an exponential-notation literal
#define PRINTF_CONCATENATE(s1, s2) s1##s2
#define PRINTF_EXPAND_THEN_CONCATENATE(s1, s2) PRINTF_CONCATENATE(s1, s2)
#define PRINTF_FLOAT_NOTATION_THRESHOLD PRINTF_EXPAND_THEN_CONCATENATE(1e,PRINTF_MAX_INTEGRAL_DIGITS_FOR_DECIMAL)
// internal flag definitions
#define FLAGS_ZEROPAD (1U << 0U)
#define FLAGS_LEFT (1U << 1U)
#define FLAGS_PLUS (1U << 2U)
#define FLAGS_SPACE (1U << 3U)
#define FLAGS_HASH (1U << 4U)
#define FLAGS_UPPERCASE (1U << 5U)
#define FLAGS_CHAR (1U << 6U)
#define FLAGS_SHORT (1U << 7U)
#define FLAGS_LONG (1U << 8U)
#define FLAGS_LONG_LONG (1U << 9U)
#define FLAGS_PRECISION (1U << 10U)
#define FLAGS_ADAPT_EXP (1U << 11U)
#define FLAGS_POINTER (1U << 12U)
// Note: Similar, but not identical, effect as FLAGS_HASH
#define BASE_BINARY 2
#define BASE_OCTAL 8
#define BASE_DECIMAL 10
#define BASE_HEX 16
typedef uint8_t numeric_base_t;
#include <float.h>
#define DOUBLE_SIZE_IN_BITS 64
typedef uint64_t double_uint_t;
#define DOUBLE_EXPONENT_MASK 0x7FFU
#define DOUBLE_BASE_EXPONENT 1023
#define DOUBLE_STORED_MANTISSA_BITS (DBL_MANT_DIG - 1)
typedef union {
double_uint_t U;
double F;
} double_with_bit_access;
// This is unnecessary in C99, since compound initializers can be used,
// but: 1. Some compilers are finicky about this; 2. Some people may want to convert this to C89;
// 3. If you try to use it as C++, only C++20 supports compound literals
static inline double_with_bit_access get_bit_access(double x)
{
double_with_bit_access dwba;
dwba.F = x;
return dwba;
}
static inline int get_sign(double x)
{
// The sign is stored in the highest bit
return get_bit_access(x).U >> (DOUBLE_SIZE_IN_BITS - 1);
}
static inline int get_exp2(double_with_bit_access x)
{
// The exponent in an IEEE-754 floating-point number occupies a contiguous
// sequence of bits (e.g. 52..62 for 64-bit doubles), but with a non-trivial representation: An
// unsigned offset from some negative value (with the extremal offset values reserved for
// special use).
return (int)((x.U >> DOUBLE_STORED_MANTISSA_BITS ) & DOUBLE_EXPONENT_MASK) - DOUBLE_BASE_EXPONENT;
}
#define PRINTF_ABS(_x) ( (_x) > 0 ? (_x) : -(_x) )
// Note in particular the behavior here on LONG_MIN or LLONG_MIN; it is valid
// and well-defined, but if you're not careful you can easily trigger undefined
// behavior with -LONG_MIN or -LLONG_MIN
#define ABS_FOR_PRINTING(_x) ((printf_unsigned_value_t) ( (_x) > 0 ? (_x) : -((printf_signed_value_t)_x) ))
// output function type
typedef void (*out_fct_type)(char character, void* buffer, unsigned int idx, unsigned int maxlen);
// wrapper (used as buffer) for output function type
typedef struct {
void (*fct)(char character, void* arg);
void* arg;
} out_function_wrapper_type;
// internal buffer output
static inline void out_buffer(char character, void* buffer, unsigned int idx, unsigned int maxlen)
{
if (idx < maxlen) {
((char*)buffer)[idx] = character;
}
}
// internal null output
static inline void out_discard(char character, void* buffer, unsigned int idx, unsigned int maxlen)
{
(void)character; (void)buffer; (void)idx; (void)maxlen;
}
// internal secure strlen
// @return The length of the string (excluding the terminating 0) limited by 'maxsize'
static inline unsigned int strnlen_s_(const char* str, unsigned int maxsize)
{
const char* s;
for (s = str; *s && maxsize--; ++s);
return (unsigned int)(s - str);
}
// internal test if char is a digit (0-9)
// @return true if char is a digit
static inline bool is_digit_(char ch)
{
return (ch >= '0') && (ch <= '9');
}
// internal ASCII string to unsigned int conversion
static unsigned int atoi_(const char** str)
{
unsigned int i = 0U;
while (is_digit_(**str)) {
i = i * 10U + (unsigned int)(*((*str)++) - '0');
}
return i;
}
// output the specified string in reverse, taking care of any zero-padding
static unsigned int out_rev_(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, const char* buf, unsigned int len, unsigned int width, unsigned int flags)
{
const unsigned int start_idx = idx;
// pad spaces up to given width
if (!(flags & FLAGS_LEFT) && !(flags & FLAGS_ZEROPAD)) {
for (unsigned int i = len; i < width; i++) {
out(' ', buffer, idx++, maxlen);
}
}
// reverse string
while (len) {
out(buf[--len], buffer, idx++, maxlen);
}
// append pad spaces up to given width
if (flags & FLAGS_LEFT) {
while (idx - start_idx < width) {
out(' ', buffer, idx++, maxlen);
}
}
return idx;
}
// Invoked by print_integer after the actual number has been printed, performing necessary
// work on the number's prefix (as the number is initially printed in reverse order)
static unsigned int print_integer_finalization(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, char* buf, unsigned int len, bool negative, numeric_base_t base, unsigned int precision, unsigned int width, unsigned int flags)
{
unsigned int unpadded_len = len;
// pad with leading zeros
{
if (!(flags & FLAGS_LEFT)) {
if (width && (flags & FLAGS_ZEROPAD) && (negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
width--;
}
while ((flags & FLAGS_ZEROPAD) && (len < width) && (len < PRINTF_INTEGER_BUFFER_SIZE)) {
buf[len++] = '0';
}
}
while ((len < precision) && (len < PRINTF_INTEGER_BUFFER_SIZE)) {
buf[len++] = '0';
}
if (base == BASE_OCTAL && (len > unpadded_len)) {
// Since we've written some zeros, we've satisfied the alternative format leading space requirement
flags &= ~FLAGS_HASH;
}
}
// handle hash
if (flags & (FLAGS_HASH | FLAGS_POINTER)) {
if (!(flags & FLAGS_PRECISION) && len && ((len == precision) || (len == width))) {
// Let's take back some padding digits to fit in what will eventually
// be the format-specific prefix
if (unpadded_len < len) {
len--;
}
if (len && (base == BASE_HEX)) {
if (unpadded_len < len) {
len--;
}
}
}
if ((base == BASE_HEX) && !(flags & FLAGS_UPPERCASE) && (len < PRINTF_INTEGER_BUFFER_SIZE)) {
buf[len++] = 'x';
}
else if ((base == BASE_HEX) && (flags & FLAGS_UPPERCASE) && (len < PRINTF_INTEGER_BUFFER_SIZE)) {
buf[len++] = 'X';
}
else if ((base == BASE_BINARY) && (len < PRINTF_INTEGER_BUFFER_SIZE)) {
buf[len++] = 'b';
}
if (len < PRINTF_INTEGER_BUFFER_SIZE) {
buf[len++] = '0';
}
}
if (len < PRINTF_INTEGER_BUFFER_SIZE) {
if (negative) {
buf[len++] = '-';
}
else if (flags & FLAGS_PLUS) {
buf[len++] = '+'; // ignore the space if the '+' exists
}
else if (flags & FLAGS_SPACE) {
buf[len++] = ' ';
}
}
return out_rev_(out, buffer, idx, maxlen, buf, len, width, flags);
}
// An internal itoa-like function
static unsigned int print_integer(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, printf_unsigned_value_t value, bool negative, numeric_base_t base, unsigned int precision, unsigned int width, unsigned int flags)
{
char buf[PRINTF_INTEGER_BUFFER_SIZE];
unsigned int len = 0U;
if (!value) {
if ( !(flags & FLAGS_PRECISION) ) {
buf[len++] = '0';
flags &= ~FLAGS_HASH;
// We drop this flag this since either the alternative and regular modes of the specifier
// don't differ on 0 values, or (in the case of octal) we've already provided the special
// handling for this mode.
}
else if (base == BASE_HEX) {
flags &= ~FLAGS_HASH;
// We drop this flag this since either the alternative and regular modes of the specifier
// don't differ on 0 values
}
}
else {
do {
const char digit = (char)(value % base);
buf[len++] = (char)(digit < 10 ? '0' + digit : (flags & FLAGS_UPPERCASE ? 'A' : 'a') + digit - 10);
value /= base;
} while (value && (len < PRINTF_INTEGER_BUFFER_SIZE));
}
return print_integer_finalization(out, buffer, idx, maxlen, buf, len, negative, base, precision, width, flags);
}
struct double_components {
int_fast64_t integral;
int_fast64_t fractional;
bool is_negative;
};
#define NUM_DECIMAL_DIGITS_IN_INT64_T 18
#define PRINTF_MAX_PRECOMPUTED_POWER_OF_10 NUM_DECIMAL_DIGITS_IN_INT64_T
static const double powers_of_10[NUM_DECIMAL_DIGITS_IN_INT64_T] = {
1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08,
1e09, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17
};
#define PRINTF_MAX_SUPPORTED_PRECISION NUM_DECIMAL_DIGITS_IN_INT64_T - 1
// Break up a double number - which is known to be a finite non-negative number -
// into its base-10 parts: integral - before the decimal point, and fractional - after it.
// Taken the precision into account, but does not change it even internally.
static struct double_components get_components(double number, unsigned int precision)
{
struct double_components number_;
number_.is_negative = get_sign(number);
double abs_number = (number_.is_negative) ? -number : number;
number_.integral = (int_fast64_t)abs_number;
double remainder = (abs_number - number_.integral) * powers_of_10[precision];
number_.fractional = (int_fast64_t)remainder;
remainder -= (double) number_.fractional;
if (remainder > 0.5) {
++number_.fractional;
// handle rollover, e.g. case 0.99 with precision 1 is 1.0
if ((double) number_.fractional >= powers_of_10[precision]) {
number_.fractional = 0;
++number_.integral;
}
}
else if (remainder == 0.5) {
if ((number_.fractional == 0U) || (number_.fractional & 1U)) {
// if halfway, round up if odd OR if last digit is 0
++number_.fractional;
}
}
if (precision == 0U) {
remainder = abs_number - (double) number_.integral;
if ((!(remainder < 0.5) || (remainder > 0.5)) && (number_.integral & 1)) {
// exactly 0.5 and ODD, then round up
// 1.5 -> 2, but 2.5 -> 2
++number_.integral;
}
}
return number_;
}
struct scaling_factor {
double raw_factor;
bool multiply; // if true, need to multiply by raw_factor; otherwise need to divide by it
};
double apply_scaling(double num, struct scaling_factor normalization)
{
return normalization.multiply ? num * normalization.raw_factor : num / normalization.raw_factor;
}
double unapply_scaling(double normalized, struct scaling_factor normalization)
{
return normalization.multiply ? normalized / normalization.raw_factor : normalized * normalization.raw_factor;
}
struct scaling_factor update_normalization(struct scaling_factor sf, double extra_multiplicative_factor)
{
struct scaling_factor result;
if (sf.multiply) {
result.multiply = true;
result.raw_factor = sf.raw_factor * extra_multiplicative_factor;
}
else {
int factor_exp2 = get_exp2(get_bit_access(sf.raw_factor));
int extra_factor_exp2 = get_exp2(get_bit_access(extra_multiplicative_factor));
// Divide the larger-exponent raw raw_factor by the smaller
if (PRINTF_ABS(factor_exp2) > PRINTF_ABS(extra_factor_exp2)) {
result.multiply = false;
result.raw_factor = sf.raw_factor / extra_multiplicative_factor;
}
else {
result.multiply = true;
result.raw_factor = extra_multiplicative_factor / sf.raw_factor;
}
}
return result;
}
static struct double_components get_normalized_components(bool negative, unsigned int precision, double non_normalized, struct scaling_factor normalization)
{
struct double_components components;
components.is_negative = negative;
components.integral = (int_fast64_t) apply_scaling(non_normalized, normalization);
double remainder = non_normalized - unapply_scaling((double) components.integral, normalization);
double prec_power_of_10 = powers_of_10[precision];
struct scaling_factor account_for_precision = update_normalization(normalization, prec_power_of_10);
double scaled_remainder = apply_scaling(remainder, account_for_precision);
double rounding_threshold = 0.5;
if (precision == 0U) {
components.fractional = 0;
components.integral += (scaled_remainder >= rounding_threshold);
if (scaled_remainder == rounding_threshold) {
// banker's rounding: Round towards the even number (making the mean error 0)
components.integral &= ~((int_fast64_t) 0x1);
}
}
else {
components.fractional = (int_fast64_t) scaled_remainder;
scaled_remainder -= components.fractional;
components.fractional += (scaled_remainder >= rounding_threshold);
if (scaled_remainder == rounding_threshold) {
// banker's rounding: Round towards the even number (making the mean error 0)
components.fractional &= ~((int_fast64_t) 0x1);
}
// handle rollover, e.g. the case of 0.99 with precision 1 becoming (0,100),
// and must then be corrected into (1, 0).
if ((double) components.fractional >= prec_power_of_10) {
components.fractional = 0;
++components.integral;
}
}
return components;
}
static unsigned int print_broken_up_decimal(
struct double_components number_, out_fct_type out, char *buffer, unsigned int idx, unsigned int maxlen, unsigned int precision,
unsigned int width, unsigned int flags, char *buf, unsigned int len)
{
if (precision != 0U) {
// do fractional part, as an unsigned number
unsigned int count = precision;
if (flags & FLAGS_ADAPT_EXP && !(flags & FLAGS_HASH)) {
// %g/%G mandates we skip the trailing 0 digits...
if (number_.fractional > 0) {
while(true) {
int_fast64_t digit = number_.fractional % 10U;
if (digit != 0) {
break;
}
--count;
number_.fractional /= 10U;
}
}
// ... and even the decimal point if there are no
// non-zero fractional part digits (see below)
}
if (number_.fractional > 0 || !(flags & FLAGS_ADAPT_EXP) || (flags & FLAGS_HASH) ) {
while (len < PRINTF_FTOA_BUFFER_SIZE) {
--count;
buf[len++] = (char)('0' + number_.fractional % 10U);
if (!(number_.fractional /= 10U)) {
break;
}
}
// add extra 0s
while ((len < PRINTF_FTOA_BUFFER_SIZE) && (count-- > 0U)) {
buf[len++] = '0';
}
if (len < PRINTF_FTOA_BUFFER_SIZE) {
buf[len++] = '.';
}
}
}
else {
if (flags & FLAGS_HASH) {
if (len < PRINTF_FTOA_BUFFER_SIZE) {
buf[len++] = '.';
}
}
}
// Write the integer part of the number (it comes after the fractional
// since the character order is reversed)
while (len < PRINTF_FTOA_BUFFER_SIZE) {
buf[len++] = (char)('0' + (number_.integral % 10));
if (!(number_.integral /= 10)) {
break;
}
}
// pad leading zeros
if (!(flags & FLAGS_LEFT) && (flags & FLAGS_ZEROPAD)) {
if (width && (number_.is_negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
width--;
}
while ((len < width) && (len < PRINTF_FTOA_BUFFER_SIZE)) {
buf[len++] = '0';
}
}
if (len < PRINTF_FTOA_BUFFER_SIZE) {
if (number_.is_negative) {
buf[len++] = '-';
}
else if (flags & FLAGS_PLUS) {
buf[len++] = '+'; // ignore the space if the '+' exists
}
else if (flags & FLAGS_SPACE) {
buf[len++] = ' ';
}
}
return out_rev_(out, buffer, idx, maxlen, buf, len, width, flags);
}
// internal ftoa for fixed decimal floating point
static unsigned int print_decimal_number(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, double number, unsigned int precision, unsigned int width, unsigned int flags, char* buf, unsigned int len)
{
struct double_components value_ = get_components(number, precision);
return print_broken_up_decimal(value_, out, buffer, idx, maxlen, precision, width, flags, buf, len);
}
// internal ftoa variant for exponential floating-point type, contributed by Martijn Jasperse <m.jasperse@gmail.com>
static unsigned int print_exponential_number(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, double number, unsigned int precision, unsigned int width, unsigned int flags, char* buf, unsigned int len)
{
const bool negative = get_sign(number);
// This number will decrease gradually (by factors of 10) as we "extract" the exponent out of it
double abs_number = negative ? -number : number;
int exp10;
bool abs_exp10_covered_by_powers_table;
struct scaling_factor normalization;
// Determine the decimal exponent
if (abs_number == 0.0) {
// TODO: This is a special-case for 0.0 (and -0.0); but proper handling is required for denormals more generally.
exp10 = 0; // ... and no need to set a normalization factor or check the powers table
}
else {
double_with_bit_access conv = get_bit_access(abs_number);
{
// based on the algorithm by David Gay (https://www.ampl.com/netlib/fp/dtoa.c)
int exp2 = get_exp2(conv);
// drop the exponent, so conv.F comes into the range [1,2)
conv.U = (conv.U & (( (double_uint_t)(1) << DOUBLE_STORED_MANTISSA_BITS) - 1U)) | ((double_uint_t) DOUBLE_BASE_EXPONENT << DOUBLE_STORED_MANTISSA_BITS);
// now approximate log10 from the log2 integer part and an expansion of ln around 1.5
exp10 = (int)(0.1760912590558 + exp2 * 0.301029995663981 + (conv.F - 1.5) * 0.289529654602168);
// now we want to compute 10^exp10 but we want to be sure it won't overflow
exp2 = (int)(exp10 * 3.321928094887362 + 0.5);
const double z = exp10 * 2.302585092994046 - exp2 * 0.6931471805599453;
const double z2 = z * z;
conv.U = ((double_uint_t)(exp2) + DOUBLE_BASE_EXPONENT) << DOUBLE_STORED_MANTISSA_BITS;
// compute exp(z) using continued fractions, see https://en.wikipedia.org/wiki/Exponential_function#Continued_fractions_for_ex
conv.F *= 1 + 2 * z / (2 - z + (z2 / (6 + (z2 / (10 + z2 / 14)))));
// correct for rounding errors
if (abs_number < conv.F) {
exp10--;
conv.F /= 10;
}
}
abs_exp10_covered_by_powers_table = PRINTF_ABS(exp10) < PRINTF_MAX_PRECOMPUTED_POWER_OF_10;
normalization.raw_factor = abs_exp10_covered_by_powers_table ? powers_of_10[PRINTF_ABS(exp10)] : conv.F;
}
// We now begin accounting for the widths of the two parts of our printed field:
// the decimal part after decimal exponent extraction, and the base-10 exponent part.
// For both of these, the value of 0 has a special meaning, but not the same one:
// a 0 exponent-part width means "don't print the exponent"; a 0 decimal-part width
// means "use as many characters as necessary".
bool fall_back_to_decimal_only_mode = false;
if (flags & FLAGS_ADAPT_EXP) {
int required_significant_digits = (precision == 0) ? 1 : (int) precision;
// Should we want to fall-back to "%f" mode, and only print the decimal part?
fall_back_to_decimal_only_mode = (exp10 >= -4 && exp10 < required_significant_digits);
// Now, let's adjust the precision
// This also decided how we adjust the precision value - as in "%g" mode,
// "precision" is the number of _significant digits_, and this is when we "translate"
// the precision value to an actual number of decimal digits.
int precision_ = (fall_back_to_decimal_only_mode) ?
(int) precision - 1 - exp10 :
(int) precision - 1; // the presence of the exponent ensures only one significant digit comes before the decimal point
precision = (precision_ > 0 ? (unsigned) precision_ : 0U);
flags |= FLAGS_PRECISION; // make sure print_broken_up_decimal respects our choice above
}
normalization.multiply = (exp10 < 0 && abs_exp10_covered_by_powers_table);
bool should_skip_normalization = (fall_back_to_decimal_only_mode || exp10 == 0);
struct double_components decimal_part_components =
should_skip_normalization ?
get_components(negative ? -abs_number : abs_number, precision) :
get_normalized_components(negative, precision, abs_number, normalization);
// Account for roll-over, e.g. rounding from 9.99 to 100.0 - which effects
// the exponent and may require additional tweaking of the parts
if (fall_back_to_decimal_only_mode) {
if ( (flags & FLAGS_ADAPT_EXP) && exp10 >= -1 && decimal_part_components.integral == powers_of_10[exp10 + 1]) {
exp10++; // Not strictly necessary, since exp10 is no longer really used
precision--;
// ... and it should already be the case that decimal_part_components.fractional == 0
}
// TODO: What about rollover strictly within the fractional part?
}
else {
if (decimal_part_components.integral >= 10) {
exp10++;
decimal_part_components.integral = 1;
decimal_part_components.fractional = 0;
}
}
// the exp10 format is "E%+03d" and largest possible exp10 value for a 64-bit double
// is "307" (for 2^1023), so we set aside 4-5 characters overall
unsigned int exp10_part_width = fall_back_to_decimal_only_mode ? 0U : (PRINTF_ABS(exp10) < 100) ? 4U : 5U;
unsigned int decimal_part_width =
((flags & FLAGS_LEFT) && exp10_part_width) ?
// We're padding on the right, so the width constraint is the exponent part's
// problem, not the decimal part's, so we'll use as many characters as we need:
0U :
// We're padding on the left; so the width constraint is the decimal part's
// problem. Well, can both the decimal part and the exponent part fit within our overall width?
((width > exp10_part_width) ?
// Yes, so we limit our decimal part's width.
// (Note this is trivially valid even if we've fallen back to "%f" mode)
width - exp10_part_width :
// No; we just give up on any restriction on the decimal part and use as many
// characters as we need
0U);
const unsigned int start_idx = idx;
idx = print_broken_up_decimal(decimal_part_components, out, buffer, idx, maxlen, precision, decimal_part_width, flags, buf, len);
if (! fall_back_to_decimal_only_mode) {
out((flags & FLAGS_UPPERCASE) ? 'E' : 'e', buffer, idx++, maxlen);
idx = print_integer(out, buffer, idx, maxlen,
ABS_FOR_PRINTING(exp10),
exp10 < 0, 10, 0, exp10_part_width - 1,
FLAGS_ZEROPAD | FLAGS_PLUS);
if (flags & FLAGS_LEFT) {
// We need to right-pad with spaces to meet the width requirement
while (idx - start_idx < width) out(' ', buffer, idx++, maxlen);
}
}
return idx;
}
static unsigned int print_floating_point(out_fct_type out, char* buffer, unsigned int idx, unsigned int maxlen, double value, unsigned int precision, unsigned int width, unsigned int flags, bool prefer_exponential)
{
char buf[PRINTF_FTOA_BUFFER_SIZE];
unsigned int len = 0U;
// test for special values
if (value != value)
return out_rev_(out, buffer, idx, maxlen, "nan", 3, width, flags);
if (value < -DBL_MAX)
return out_rev_(out, buffer, idx, maxlen, "fni-", 4, width, flags);
if (value > DBL_MAX)
return out_rev_(out, buffer, idx, maxlen, (flags & FLAGS_PLUS) ? "fni+" : "fni", (flags & FLAGS_PLUS) ? 4U : 3U, width, flags);
if (!prefer_exponential && ((value > PRINTF_FLOAT_NOTATION_THRESHOLD) || (value < -PRINTF_FLOAT_NOTATION_THRESHOLD))) {
// The required behavior of standard printf is to print _every_ integral-part digit -- which could mean
// printing hundreds of characters, overflowing any fixed internal buffer and necessitating a more complicated
// implementation.
return print_exponential_number(out, buffer, idx, maxlen, value, precision, width, flags, buf, len);
}
// set default precision, if not set explicitly
if (!(flags & FLAGS_PRECISION)) {
precision = PRINTF_DEFAULT_FLOAT_PRECISION;
}
// limit precision so that our integer holding the fractional part does not overflow
while ((len < PRINTF_FTOA_BUFFER_SIZE) && (precision > PRINTF_MAX_SUPPORTED_PRECISION)) {
buf[len++] = '0'; // This respects the precision in terms of result length only
precision--;
}
return
prefer_exponential ?
print_exponential_number(out, buffer, idx, maxlen, value, precision, width, flags, buf, len) :
print_decimal_number(out, buffer, idx, maxlen, value, precision, width, flags, buf, len);
}
// internal vsnprintf
static int __vsnprintf(out_fct_type out, char* buffer, const unsigned int maxlen, const char* format, va_list va)
{
unsigned int flags, width, precision, n;
unsigned int idx = 0U;
if (!buffer) {
// use null output function
out = out_discard;
}
while (*format)
{
// format specifier? %[flags][width][.precision][length]
if (*format != '%') {
// no
out(*format, buffer, idx++, maxlen);
format++;
continue;
}
else {
// yes, evaluate it
format++;
}
// evaluate flags
flags = 0U;
do {
switch (*format) {
case '0': flags |= FLAGS_ZEROPAD; format++; n = 1U; break;
case '-': flags |= FLAGS_LEFT; format++; n = 1U; break;
case '+': flags |= FLAGS_PLUS; format++; n = 1U; break;
case ' ': flags |= FLAGS_SPACE; format++; n = 1U; break;
case '#': flags |= FLAGS_HASH; format++; n = 1U; break;
default : n = 0U; break;
}
} while (n);
// evaluate width field
width = 0U;
if (is_digit_(*format)) {
width = atoi_(&format);
}
else if (*format == '*') {
const int w = va_arg(va, int);
if (w < 0) {
flags |= FLAGS_LEFT; // reverse padding
width = (unsigned int)-w;
}
else {
width = (unsigned int)w;
}
format++;
}
// evaluate precision field
precision = 0U;
if (*format == '.') {
flags |= FLAGS_PRECISION;
format++;
if (is_digit_(*format)) {
precision = atoi_(&format);
}
else if (*format == '*') {
const int precision_ = (int)va_arg(va, int);
precision = precision_ > 0 ? (unsigned int)precision_ : 0U;
format++;
}
}
// evaluate length field
switch (*format) {
case 'l' :
flags |= FLAGS_LONG;
format++;
if (*format == 'l') {
flags |= FLAGS_LONG_LONG;
format++;
}
break;
case 'h' :
flags |= FLAGS_SHORT;
format++;
if (*format == 'h') {
flags |= FLAGS_CHAR;
format++;
}
break;
case 't' :
flags |= (sizeof(ptrdiff_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
format++;
break;
case 'j' :
flags |= (sizeof(intmax_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
format++;
break;
case 'z' :
flags |= (sizeof(unsigned int) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
format++;
break;
default:
break;
}
// evaluate specifier
switch (*format) {
case 'd' :
case 'i' :
case 'u' :
case 'x' :
case 'X' :
case 'o' :
case 'b' : {
// set the base
numeric_base_t base;
if (*format == 'x' || *format == 'X') {
base = BASE_HEX;
}
else if (*format == 'o') {
base = BASE_OCTAL;
}
else if (*format == 'b') {
base = BASE_BINARY;
}
else {
base = BASE_DECIMAL;
flags &= ~FLAGS_HASH; // no hash for dec format
}
// uppercase
if (*format == 'X') {
flags |= FLAGS_UPPERCASE;
}
// no plus or space flag for u, x, X, o, b
if ((*format != 'i') && (*format != 'd')) {
flags &= ~(FLAGS_PLUS | FLAGS_SPACE);
}
// ignore '0' flag when precision is given
if (flags & FLAGS_PRECISION) {
flags &= ~FLAGS_ZEROPAD;
}
// convert the integer
if ((*format == 'i') || (*format == 'd')) {
// signed
if (flags & FLAGS_LONG_LONG) {
const long long value = va_arg(va, long long);
idx = print_integer(out, buffer, idx, maxlen, ABS_FOR_PRINTING(value), value < 0, base, precision, width, flags);
}
else if (flags & FLAGS_LONG) {
const long value = va_arg(va, long);
idx = print_integer(out, buffer, idx, maxlen, ABS_FOR_PRINTING(value), value < 0, base, precision, width, flags);
}
else {
const int value = (flags & FLAGS_CHAR) ? (signed char)va_arg(va, int) : (flags & FLAGS_SHORT) ? (short int)va_arg(va, int) : va_arg(va, int);
idx = print_integer(out, buffer, idx, maxlen, ABS_FOR_PRINTING(value), value < 0, base, precision, width, flags);
}
}
else {
// unsigned
if (flags & FLAGS_LONG_LONG) {
idx = print_integer(out, buffer, idx, maxlen, (printf_unsigned_value_t) va_arg(va, unsigned long long), false, base, precision, width, flags);
}
else if (flags & FLAGS_LONG) {
idx = print_integer(out, buffer, idx, maxlen, (printf_unsigned_value_t) va_arg(va, unsigned long), false, base, precision, width, flags);
}
else {
const unsigned int value = (flags & FLAGS_CHAR) ? (unsigned char)va_arg(va, unsigned int) : (flags & FLAGS_SHORT) ? (unsigned short int)va_arg(va, unsigned int) : va_arg(va, unsigned int);
idx = print_integer(out, buffer, idx, maxlen, (printf_unsigned_value_t) value, false, base, precision, width, flags);
}
}
format++;
break;
}
case 'f' :
case 'F' :
if (*format == 'F') flags |= FLAGS_UPPERCASE;
idx = print_floating_point(out, buffer, idx, maxlen, va_arg(va, double), precision, width, flags, PRINTF_PREFER_DECIMAL);
format++;
break;
case 'e':
case 'E':
case 'g':
case 'G':
if ((*format == 'g')||(*format == 'G')) flags |= FLAGS_ADAPT_EXP;
if ((*format == 'E')||(*format == 'G')) flags |= FLAGS_UPPERCASE;
idx = print_floating_point(out, buffer, idx, maxlen, va_arg(va, double), precision, width, flags, PRINTF_PREFER_EXPONENTIAL);
format++;
break;
case 'c' : {
unsigned int l = 1U;
// pre padding
if (!(flags & FLAGS_LEFT)) {
while (l++ < width) {
out(' ', buffer, idx++, maxlen);
}
}
// char output
out((char)va_arg(va, int), buffer, idx++, maxlen);
// post padding
if (flags & FLAGS_LEFT) {
while (l++ < width) {
out(' ', buffer, idx++, maxlen);
}
}
format++;
break;
}
case 's' : {
const char* p = va_arg(va, char*);
if (p == NULL) {
idx = out_rev_(out, buffer, idx, maxlen, ")llun(", 6, width, flags);
}
else {
unsigned int l = strnlen_s_(p, precision ? precision : (unsigned int)-1);
// pre padding
if (flags & FLAGS_PRECISION) {
l = (l < precision ? l : precision);
}
if (!(flags & FLAGS_LEFT)) {
while (l++ < width) {
out(' ', buffer, idx++, maxlen);
}
}
// string output
while ((*p != 0) && (!(flags & FLAGS_PRECISION) || precision--)) {
out(*(p++), buffer, idx++, maxlen);
}
// post padding
if (flags & FLAGS_LEFT) {
while (l++ < width) {
out(' ', buffer, idx++, maxlen);
}
}
}
format++;
break;
}
case 'p' : {
width = sizeof(void*) * 2U + 2; // 2 hex chars per byte + the "0x" prefix
flags |= FLAGS_ZEROPAD | FLAGS_POINTER;
uintptr_t value = (uintptr_t)va_arg(va, void*);
idx = (value == (uintptr_t) NULL) ?
out_rev_(out, buffer, idx, maxlen, ")lin(", 5, width, flags) :
print_integer(out, buffer, idx, maxlen, (printf_unsigned_value_t) value, false, BASE_HEX, precision, width, flags);
format++;
break;
}
case '%' :
out('%', buffer, idx++, maxlen);
format++;
break;
default :
out(*format, buffer, idx++, maxlen);
format++;
break;
}
}
// termination
out((char)0, buffer, idx < maxlen ? idx : maxlen - 1U, maxlen);
// return written chars without terminating \0
return (int)idx;
}
/**
* This function will fill a formatted string to buffer.
*
* @param buf is the buffer to save formatted string.
*
* @param size is the size of buffer.
*
* @param fmt is the format parameters.
*
* @param args is a list of variable parameters.
*
* @return The number of characters actually written to buffer.
*/
signed int rt_vsnprintf(char *buf, unsigned int size, const char *fmt, va_list args)
{
return __vsnprintf(out_buffer, buf, size, fmt, args);
}
printf实现
#include <stdarg.h>
#define PRINT_BUFFER_SIZE 512
char printf_string[PRINT_BUFFER_SIZE];
void my_printf(char *fmt,...)
{
va_list ap;
uint32_t length;
va_start(ap,fmt);
length = rt_vsnprintf(printf_string,PRINT_BUFFER_SIZE,fmt,ap);
HAL_UART_Transmit(&huart1, (uint8_t *) printf_string, length, HAL_MAX_DELAY);
va_end(ap);
}
总结
这个自行构造的printf函数是在给的缓冲区里组装打印报文的，自行设置缓存区大小，以及打印输出方式，这里用的是stm32的串口1输出，使用的是hal库。
