1 #include <limits.h> 2 #include "libm.h" 3 ilogb(double x)4int 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 } 27