ref: e4509d40cc9759baddf1c2571247b95d2f5b61a5
dir: /sys/src/ape/lib/ap/plan9/frexp.c/
#include <math.h> #include <errno.h> #define _RESEARCH_SOURCE #include <float.h> #define MASK 0x7ffL #define SHIFT 20 #define BIAS 1022L #define SIG 52 typedef union { double d; struct { #ifdef IEEE_8087 long ls; long ms; #else long ms; long ls; #endif }; } Cheat; double frexp(double d, int *ep) { Cheat x, a; *ep = 0; /* order matters: only isNaN can operate on NaN */ if(isNaN(d) || isInf(d, 0) || d == 0) return d; x.d = d; a.d = fabs(d); if((a.ms >> SHIFT) == 0){ /* normalize subnormal numbers */ x.d = (double)(1ULL<<SIG) * d; *ep = -SIG; } *ep = ((x.ms >> SHIFT) & MASK) - BIAS; x.ms &= ~(MASK << SHIFT); x.ms |= BIAS << SHIFT; return x.d; } double ldexp(double d, int e) { Cheat x; if(d == 0) return 0; x.d = d; e += (x.ms >> SHIFT) & MASK; if(e <= 0) return 0; if(e >= MASK){ errno = ERANGE; if(d < 0) return -HUGE_VAL; return HUGE_VAL; } x.ms &= ~(MASK << SHIFT); x.ms |= (long)e << SHIFT; return x.d; } double modf(double d, double *ip) { double f; Cheat x; int e; x.d = d; e = (x.ms >> SHIFT) & MASK; if(e == MASK){ *ip = d; if(x.ls != 0 || (x.ms & 0xfffffL) != 0) /* NaN */ return d; /* ±Inf */ x.ms &= 0x80000000L; return x.d; } if(d < 1) { if(d < 0) { f = modf(-d, ip); *ip = -*ip; return -f; } *ip = 0; return d; } e -= BIAS; if(e <= SHIFT+1) { x.ms &= ~(0x1fffffL >> e); x.ls = 0; } else if(e <= SHIFT+33) x.ls &= ~(0x7fffffffL >> (e-SHIFT-2)); *ip = x.d; return d - x.d; }