diff options
Diffstat (limited to 'libm')
| -rw-r--r-- | libm/s_ilogb.c | 47 |
1 files changed, 31 insertions, 16 deletions
diff --git a/libm/s_ilogb.c b/libm/s_ilogb.c index ce3029667..259ae7b55 100644 --- a/libm/s_ilogb.c +++ b/libm/s_ilogb.c @@ -10,9 +10,10 @@ */ /* ilogb(double x) - * return the binary exponent of non-zero x - * ilogb(0) = 0x80000001 - * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) + * return the binary exponent of x + * ilogb(+-0) = FP_ILOGB0 + * ilogb(+-inf) = INT_MAX + * ilogb(NaN) = FP_ILOGBNAN (no signal is raised) */ #include "math.h" @@ -22,21 +23,35 @@ int ilogb(double x) { int32_t hx,lx,ix; - GET_HIGH_WORD(hx,x); + GET_HIGH_WORD(hx, x); hx &= 0x7fffffff; - if(hx<0x00100000) { - GET_LOW_WORD(lx,x); - if((hx|lx)==0) - return 0x80000001; /* ilogb(0) = 0x80000001 */ - else /* subnormal x */ - if(hx==0) { - for (ix = -1043; lx>0; lx<<=1) ix -=1; - } else { - for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; + + if (hx < 0x00100000) { + GET_LOW_WORD(lx, x); + if ((hx|lx)==0) /* +-0, ilogb(0) = FP_ILOGB0 */ + return FP_ILOGB0; + /* subnormal x */ + ix = -1043; + if (hx != 0) { + ix = -1022; + lx = (hx << 11); } - return ix; + /* each leading zero mantissa bit makes exponent smaller */ + for (; lx > 0; lx <<= 1) + ix--; + return ix; } - else if (hx<0x7ff00000) return (hx>>20)-1023; - else return 0x7fffffff; + + if (hx < 0x7ff00000) /* normal x */ + return (hx>>20) - 1023; + + if (FP_ILOGBNAN != (~0U >> 1)) { + GET_LOW_WORD(lx, x); + if (hx == 0x7ff00000 && lx == 0) /* +-inf */ + return ~0U >> 1; /* = INT_MAX */ + } + + /* NAN. ilogb(NAN) = FP_ILOGBNAN */ + return FP_ILOGBNAN; } libm_hidden_def(ilogb) |