| 1 | #include <limits.h> |
| 2 | #include "libm.h" |
| 3 | |
| 4 | int ilogb(double x) |
| 5 | { |
| 6 | #pragma STDC FENV_ACCESS ON |
| 7 | union {double f; uint64_t i;} u = {x}; |
| 8 | uint64_t i = u.i; |
| 9 | int e = i>>52 & 0x7ff; |
| 10 | |
| 11 | if (!e) { |
| 12 | i <<= 12; |
| 13 | if (i == 0) { |
| 14 | FORCE_EVAL(0/0.0f); |
| 15 | return FP_ILOGB0; |
| 16 | } |
| 17 | /* subnormal x */ |
| 18 | for (e = -0x3ff; i>>63 == 0; e--, i<<=1); |
| 19 | return e; |
| 20 | } |
| 21 | if (e == 0x7ff) { |
| 22 | FORCE_EVAL(0/0.0f); |
| 23 | return i<<12 ? FP_ILOGBNAN : INT_MAX; |
| 24 | } |
| 25 | return e - 0x3ff; |
| 26 | } |