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Fixed float to integer punning in nanoprintf.c #590

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Fixed float to integer punning in nanoprintf.c #590

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22 changes: 16 additions & 6 deletions src/libc/nanoprintf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -485,11 +485,16 @@ static int npf_fsplit_abs(float f, uint64_t *out_int_part, uint64_t *out_frac_pa
grisu2 (https://bit.ly/2JgMggX) and ryu (https://bit.ly/2RLXSg0)
are fast + precise + round, but require large lookup tables. */

#if 0
uint32_t f_bits; { // union-cast is UB, let compiler optimize byte-copy loop.
char const *src = (char const *)&f;
char *dst = (char *)&f_bits;
for (unsigned i = 0; i < sizeof(f_bits); ++i) { dst[i] = src[i]; }
}
#else
uint32_t f_bits;
__builtin_memcpy(&f_bits, &f, sizeof(uint32_t));
#endif

int const exponent =
((int)((f_bits >> NPF_MANTISSA_BITS) & ((1u << NPF_EXPONENT_BITS) - 1u)) -
Expand Down Expand Up @@ -549,12 +554,17 @@ static int npf_fsplit_abs(float f, uint64_t *out_int_part, uint64_t *out_frac_pa
}

static int npf_ftoa_rev(char *buf, float f, char case_adj, int *out_frac_chars) {
uint32_t f_bits; { // union-cast is UB, let compiler optimize byte-copy loop.
char const *src = (char const *)&f;
char *dst = (char *)&f_bits;
for (unsigned i = 0; i < sizeof(f_bits); ++i) { dst[i] = src[i]; }
}

#if 0
uint32_t f_bits; { // union-cast is UB, let compiler optimize byte-copy loop.
char const *src = (char const *)&f;
char *dst = (char *)&f_bits;
for (unsigned i = 0; i < sizeof(f_bits); ++i) { dst[i] = src[i]; }
}
#else
uint32_t f_bits;
__builtin_memcpy(&f_bits, &f, sizeof(uint32_t));
#endif

if ((uint8_t)(f_bits >> 23) == 0xFF) {
if (f_bits & 0x7fffff) {
for (int i = 0; i < 3; ++i) { *buf++ = (char)("NAN"[i] + case_adj); }
Expand Down
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