312 lines
8.1 KiB
C
312 lines
8.1 KiB
C
/***********************************************************************
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format-float.c - Ruutine for converting a single-precision floating
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point number into a string.
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The code in this funcion was inspired from Fred Bayer's pdouble.c.
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Since pdouble.c was released as Public Domain, I'm releasing this
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code as public domain as well.
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The original code can be found in https://github.com/dhylands/format-float
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Dave Hylands
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***********************************************************************/
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#include <stdint.h>
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#include <stdlib.h>
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#include "mpconfig.h"
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#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
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#include "format-float.h"
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// 1 sign bit, 8 exponent bits, and 23 mantissa bits.
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// exponent values 0 and 255 are reserved, exponent can be 1 to 254.
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// exponent is stored with a bias of 127.
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// The min and max floats are on the order of 1x10^37 and 1x10^-37
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#define FLT_SIGN_MASK 0x80000000
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#define FLT_EXP_MASK 0x7F800000
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#define FLT_MAN_MASK 0x007FFFFF
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static const float g_pos_pow[] = {
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1e32, 1e16, 1e8, 1e4, 1e2, 1e1
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};
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static const float g_neg_pow[] = {
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1e-32, 1e-16, 1e-8, 1e-4, 1e-2, 1e-1
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};
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int format_float(float f, char *buf, size_t buf_size, char fmt, int prec, char sign) {
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char *s = buf;
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int buf_remaining = buf_size - 1;
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union {
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float f;
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uint32_t u;
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} num = {f};
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if (buf_size < 7) {
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// Smallest exp notion is -9e+99 which is 6 chars plus terminating
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// nulll.
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if (buf_size >= 2) {
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*s++ = '?';
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}
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if (buf_size >= 1) {
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*s++ = '\0';
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}
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return buf_size >= 2;
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}
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if (num.u & FLT_SIGN_MASK) {
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*s++ = '-';
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num.u &= ~FLT_SIGN_MASK;
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} else {
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if (sign) {
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*s++ = sign;
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}
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}
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buf_remaining -= (s - buf); // Adjust for sign
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if ((num.u & FLT_EXP_MASK) == FLT_EXP_MASK) {
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char uc = fmt & 0x20;
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if ((num.u & FLT_MAN_MASK) == 0) {
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*s++ = 'I' ^ uc;
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*s++ = 'N' ^ uc;
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*s++ = 'F' ^ uc;
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} else {
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*s++ = 'N' ^ uc;
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*s++ = 'A' ^ uc;
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*s++ = 'N' ^ uc;
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}
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*s = '\0';
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return s - buf;
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}
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if (prec < 0) {
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prec = 6;
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}
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char e_char = 'E' | (fmt & 0x20); // e_char will match case of fmt
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fmt |= 0x20; // Force fmt to be lowercase
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char org_fmt = fmt;
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if (fmt == 'g' && prec == 0) {
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prec = 1;
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}
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int e, e1;
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int dec = 0;
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char e_sign = '\0';
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int num_digits = 0;
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const float *pos_pow = g_pos_pow;
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const float *neg_pow = g_neg_pow;
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if (num.u == 0) {
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e = 0;
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if (fmt == 'e') {
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e_sign = '+';
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} else if (fmt == 'f') {
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num_digits = prec + 1;
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}
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} else if (num.u < 0x3f800000) { // f < 1.0
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// Build negative exponent
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for (e = 0, e1 = 32; e1; e1 >>= 1, pos_pow++, neg_pow++) {
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if (*neg_pow > num.f) {
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e += e1;
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num.f *= *pos_pow;
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}
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}
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if (num.f < 1.0F && num.f >= 0.9999995F) {
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num.f = 1.0F;
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} else {
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e++;
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num.f *= 10.0F;
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}
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// If the user specified 'g' format, and e is <= 4, then we'll switch
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// to the fixed format ('f')
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if (fmt == 'f' || (fmt == 'g' && e <= 4)) {
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fmt = 'f';
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dec = -1;
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*s++ = '0';
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if (prec + e + 1 > buf_remaining) {
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prec = buf_remaining - e - 1;
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}
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if (org_fmt == 'g') {
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prec += (e - 1);
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}
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num_digits = prec;
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if (num_digits) {
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*s++ = '.';
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while (--e && num_digits) {
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*s++ = '0';
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num_digits--;
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}
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}
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} else {
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// For e & g formats, we'll be printing the exponent, so set the
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// sign.
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e_sign = '-';
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dec = 0;
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if (prec > (buf_remaining - 6)) {
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prec = buf_remaining - 6;
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if (fmt == 'g') {
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prec++;
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}
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}
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}
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} else {
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// Build positive exponent
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for (e = 0, e1 = 32; e1; e1 >>= 1, pos_pow++, neg_pow++) {
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if (*pos_pow <= num.f) {
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e += e1;
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num.f *= *neg_pow;
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}
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}
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// If the user specified fixed format (fmt == 'f') and e makes the
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// number too big to fit into the available buffer, then we'll
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// switch to the 'e' format.
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if (fmt == 'f') {
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if (e >= buf_remaining) {
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fmt = 'e';
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} else if ((e + prec + 2) > buf_remaining) {
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prec = buf_remaining - e - 2;
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if (prec < 0) {
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// This means no decimal point, so we can add one back
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// for the decimal.
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prec++;
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}
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}
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}
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if (fmt == 'e' && prec > (buf_remaining - 6)) {
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prec = buf_remaining - 6;
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}
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// If the user specified 'g' format, and e is < prec, then we'll switch
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// to the fixed format.
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if (fmt == 'g' && e < prec) {
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fmt = 'f';
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prec -= (e + 1);
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}
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if (fmt == 'f') {
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dec = e;
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num_digits = prec + e + 1;
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} else {
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e_sign = '+';
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}
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}
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if (prec < 0) {
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// This can happen when the prec is trimmed to prevent buffer overflow
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prec = 0;
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}
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// We now have num.f as a floating point number between >= 1 and < 10
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// (or equal to zero), and e contains the absolute value of the power of
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// 10 exponent. and (dec + 1) == the number of dgits before the decimal.
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// For e, prec is # digits after the decimal
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// For f, prec is # digits after the decimal
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// For g, prec is the max number of significant digits
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//
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// For e & g there will be a single digit before the decimal
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// for f there will be e digits before the decimal
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if (fmt == 'e') {
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num_digits = prec + 1;
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} else if (fmt == 'g') {
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if (prec == 0) {
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prec = 1;
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}
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num_digits = prec;
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}
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// Print the digits of the mantissa
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for (int i = 0; i < num_digits; ++i, --dec) {
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int32_t d = num.f;
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*s++ = '0' + d;
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if (dec == 0 && prec > 0) {
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*s++ = '.';
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}
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num.f -= (float)d;
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num.f *= 10.0F;
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}
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// Round
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if (num.f >= 5.0F) {
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char *rs = s;
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rs--;
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while (1) {
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if (*rs == '.') {
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rs--;
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continue;
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}
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if (*rs < '0' || *rs > '9') {
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// + or -
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rs++; // So we sit on the digit to the right of the sign
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break;
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}
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if (*rs < '9') {
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(*rs)++;
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break;
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}
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*rs = '0';
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if (rs == buf) {
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break;
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}
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rs--;
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}
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if (*rs == '0') {
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// We need to insert a 1
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if (rs[1] == '.' && fmt != 'f') {
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// We're going to round 9.99 to 10.00
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// Move the decimal point
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rs[0] = '.';
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rs[1] = '0';
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if (e_sign == '-') {
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e--;
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} else {
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e++;
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}
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}
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s++;
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char *ss = s;
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while (ss > rs) {
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*ss = ss[-1];
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ss--;
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}
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*rs = '1';
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}
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if (num.u < 0x3f800000 && fmt == 'f') {
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// We rounded up to 1.0
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prec--;
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}
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}
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if (org_fmt == 'g' && prec > 0) {
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// Remove trailing zeros and a trailing decimal point
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while (s[-1] == '0') {
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s--;
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}
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if (s[-1] == '.') {
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s--;
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}
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}
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// Append the exponent
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if (e_sign) {
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*s++ = e_char;
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*s++ = e_sign;
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*s++ = '0' + (e / 10);
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*s++ = '0' + (e % 10);
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}
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*s = '\0';
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return s - buf;
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}
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#endif
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