114 lines
2.8 KiB
C++
114 lines
2.8 KiB
C++
/* Reprezentace float podle IEEE 754 v little endien */
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#include <stdint.h>
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typedef __SIZE_TYPE__ size_t;
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typedef union {
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float f;
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struct {
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uint32_t frac : 23;
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uint32_t exp : 8;
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uint32_t sign : 1;
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} u;
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} float_unsigned;
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typedef union {
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uint32_t u;
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struct {
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uint32_t l : 28;
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uint32_t h : 4;
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} e;
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} u2m;
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// výstupní znaky
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static const char * dec = "0123456789";
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// decimální exponent e do bufferu buff
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static size_t exp_str (char * buf, const int e) {
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size_t n = 0;
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int exp = 0, res;
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buf [n++] = 'E';
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if (e > 0) {
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buf [n++] = '+';
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exp = e;
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} else if (e < 0) {
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buf [n++] = '-';
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exp = -e;
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} else {
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buf [n++] = '+';
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buf [n++] = '0';
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buf [n++] = '0';
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return n;
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}
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n += 2;
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res = exp % 10;
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buf [n - 1] = dec [res];
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exp = exp / 10;
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res = exp % 10;
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buf [n - 2] = dec [res];
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return n;
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}
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// konstanty pro decimální normalizaci
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static const float exp_plus [] = {
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1.0e+1f, 1.0e+2f, 1.0e+4f, 1.0e+8f, 1.0e+16f, 1.0e+32f,
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};
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static const float exp_minus [] = {
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1.0e-1f, 1.0e-2f, 1.0e-4f, 1.0e-8f, 1.0e-16f, 1.0e-32f,
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};
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// decimální normalizace f do rozsahu <0.1, 1.0)
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static float f_norm (const float f, int * pe) {
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float_unsigned res;
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res.f = f;
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uint32_t s = res.u.sign; // schovej znaménko
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res.u.sign = 0u; // dál už počítej jen s absolutní hodnotou
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unsigned n = 5u;
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if (res.f >= 1.0f) {
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do {
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if (res.f >= exp_plus [n]) {
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res.f *= exp_minus [n];
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* pe += 1 << n;
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}
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} while (n--);
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res.f *= 0.1f;
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* pe += 1;
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} else {
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do {
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if (res.f < exp_minus [n]) {
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res.f *= exp_plus [n];
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* pe -= 1 << n;
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}
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} while (n--);
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}
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res.u.sign = s; // obnov znaménko
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// printf("normalized = %f, decimal exponent = %d\n", res.f, * pe);
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return res.f;
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}
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static unsigned to_str (const float f, char * buf) {
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int dec_exp = 0;
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float_unsigned fu;
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fu.f = f_norm (f, & dec_exp);
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u2m um;
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// převod formátu pro výstup číslic pomocí celočíselného násobení 10
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um.u = (fu.u.frac | (1lu << 23)) << (fu.u.exp - 122u);
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unsigned n = 0;
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if (fu.u.sign) buf [n++] = '-';
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else buf [n++] = '+';
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if (fu.f != 0.0f) {
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for (;;) { // exportuj decimální číslice
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um.u *= 10u;
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const char c = dec [um.e.h];
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um.e.h = 0u;
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if (n == 2) buf [n++] = '.';
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buf [n++] = c;
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if (n >= 10) break; // 8 platnych cislic
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}
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n += exp_str (buf + n, dec_exp - 1);
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} else { // 0.0f
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buf [n++] = '0';
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for (unsigned i=0; i<12; i++) buf[n++] = ' ';
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}
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buf [n] = '\0'; // ukončení
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return n;
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}
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#include "print.h"
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Print & Print::operator<< (const float num) {
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const unsigned n = to_str(num, buf);
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BlockDown (buf, n);
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return * this;
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}
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