diff options
Diffstat (limited to 'src/math/scalbn.c')
| -rw-r--r-- | src/math/scalbn.c | 76 |
1 files changed, 21 insertions, 55 deletions
diff --git a/src/math/scalbn.c b/src/math/scalbn.c index b51551b5..c9c7af80 100644 --- a/src/math/scalbn.c +++ b/src/math/scalbn.c @@ -1,62 +1,28 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbn.c */ -/* - * ==================================================== - * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. - * - * Developed at SunPro, a Sun Microsystems, Inc. business. - * Permission to use, copy, modify, and distribute this - * software is freely granted, provided that this notice - * is preserved. - * ==================================================== - */ -/* - * scalbn (double x, int n) - * scalbn(x,n) returns x* 2**n computed by exponent - * manipulation rather than by actually performing an - * exponentiation or a multiplication. - */ - #include "libm.h" -static const double -two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ -twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ -huge = 1.0e+300, -tiny = 1.0e-300; - double scalbn(double x, int n) { -// FIXME: k+n check depends on signed int overflow.. use unsigned hx -// TODO: when long != int: -// scalbln(x,long n) { if(n>9999)n=9999; else if(n<-9999)n=-9999; return scalbn(x,n); } -// TODO: n < -50000 ... - int32_t k,hx,lx; + double scale; - EXTRACT_WORDS(hx, lx, x); - k = (hx&0x7ff00000)>>20; /* extract exponent */ - if (k == 0) { /* 0 or subnormal x */ - if ((lx|(hx&0x7fffffff)) == 0) /* +-0 */ - return x; - x *= two54; - GET_HIGH_WORD(hx, x); - k = ((hx&0x7ff00000)>>20) - 54; - if (n < -50000) - return tiny*x; /*underflow*/ - } - if (k == 0x7ff) /* NaN or Inf */ - return x + x; - k = k + n; - if (k > 0x7fe) - return huge*copysign(huge, x); /* overflow */ - if (k > 0) { /* normal result */ - SET_HIGH_WORD(x, (hx&0x800fffff)|(k<<20)); - return x; + if (n > 1023) { + x *= 0x1p1023; + n -= 1023; + if (n > 1023) { + x *= 0x1p1023; + n -= 1023; + if (n > 1023) + return x * 0x1p1023; + } + } else if (n < -1022) { + x *= 0x1p-1022; + n += 1022; + if (n < -1022) { + x *= 0x1p-1022; + n += 1022; + if (n < -1022) + return x * 0x1p-1022; + } } - if (k <= -54) - if (n > 50000) /* in case integer overflow in n+k */ - return huge*copysign(huge, x); /*overflow*/ - return tiny*copysign(tiny, x); /*underflow*/ - k += 54; /* subnormal result */ - SET_HIGH_WORD(x, (hx&0x800fffff)|(k<<20)); - return x*twom54; + INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0); + return x * scale; } |