From: nsz Date: Mon, 19 Mar 2012 09:54:07 +0000 (+0100) Subject: simplify scalbn*.c implementations X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=commitdiff_plain;h=8051e08e10d2b739fcfcbc6bc7466e8d77fa49f1 simplify scalbn*.c implementations The old scalbn.c was wrong and slow, the new one is just slow. (scalbn(0x1p+1023,-2097) should give 0x1p-1074, but the old code gave 0) --- 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; } diff --git a/src/math/scalbnf.c b/src/math/scalbnf.c index 0a6168b0..243dafdf 100644 --- a/src/math/scalbnf.c +++ b/src/math/scalbnf.c @@ -1,54 +1,28 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbnf.c */ -/* - * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. - */ -/* - * ==================================================== - * 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. - * ==================================================== - */ - #include "libm.h" -static const float -two25 = 3.355443200e+07, /* 0x4c000000 */ -twom25 = 2.9802322388e-08, /* 0x33000000 */ -huge = 1.0e+30, -tiny = 1.0e-30; - float scalbnf(float x, int n) { - int32_t k, ix; - GET_FLOAT_WORD(ix, x); - k = (ix&0x7f800000)>>23; /* extract exponent */ - if (k == 0) { /* 0 or subnormal x */ - if ((ix&0x7fffffff) == 0) /* +-0 */ - return x; - x *= two25; - GET_FLOAT_WORD(ix, x); - k = ((ix&0x7f800000)>>23) - 25; - if (n < -50000) - return tiny*x; /*underflow*/ - } - if (k == 0xff) /* NaN or Inf */ - return x + x; - k = k + n; - if (k > 0xfe) - return huge*copysignf(huge, x); /* overflow */ - if (k > 0) { /* normal result */ - SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23)); - return x; + float scale; + + if (n > 127) { + x *= 0x1p127f; + n -= 127; + if (n > 127) { + x *= 0x1p127f; + n -= 127; + if (n > 127) + return x * 0x1p127f; + } + } else if (n < -126) { + x *= 0x1p-126f; + n += 126; + if (n < -126) { + x *= 0x1p-126f; + n += 126; + if (n < -126) + return x * 0x1p-126f; + } } - if (k <= -25) - if (n > 50000) /* in case integer overflow in n+k */ - return huge*copysignf(huge,x); /*overflow*/ - return tiny*copysignf(tiny, x); /*underflow*/ - k += 25; /* subnormal result */ - SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23)); - return x*twom25; + SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23); + return x * scale; } diff --git a/src/math/scalbnl.c b/src/math/scalbnl.c index 0ed5b7fd..a5d0adba 100644 --- a/src/math/scalbnl.c +++ b/src/math/scalbnl.c @@ -1,21 +1,3 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbnl.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. - * ==================================================== - */ -/* - * scalbnl (long double x, int n) - * scalbnl(x,n) returns x* 2**n computed by exponent - * manipulation rather than by actually performing an - * exponentiation or a multiplication. - */ - #include "libm.h" #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024 @@ -24,40 +6,31 @@ long double scalbnl(long double x, int n) return scalbn(x, n); } #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384 -static const long double -huge = 0x1p16000L, -tiny = 0x1p-16000L; - long double scalbnl(long double x, int n) { - union IEEEl2bits u; - int k; + union IEEEl2bits scale; - u.e = x; - k = u.bits.exp; /* extract exponent */ - if (k == 0) { /* 0 or subnormal x */ - if ((u.bits.manh|u.bits.manl) == 0) /* +-0 */ - return x; - u.e *= 0x1p128; - k = u.bits.exp - 128; - if (n < -50000) - return tiny*x; /*underflow*/ - } - if (k == 0x7fff) /* NaN or Inf */ - return x + x; - k = k + n; - if (k >= 0x7fff) - return huge*copysignl(huge, x); /* overflow */ - if (k > 0) { /* normal result */ - u.bits.exp = k; - return u.e; + if (n > 16383) { + x *= 0x1p16383L; + n -= 16383; + if (n > 16383) { + x *= 0x1p16383L; + n -= 16383; + if (n > 16383) + return x * 0x1p16383L; + } + } else if (n < -16382) { + x *= 0x1p-16382L; + n += 16382; + if (n < -16382) { + x *= 0x1p-16382L; + n += 16382; + if (n < -16382) + return x * 0x1p-16382L; + } } - if (k <= -128) - if (n > 50000) /* in case integer overflow in n+k */ - return huge*copysign(huge, x); /*overflow*/ - return tiny*copysign(tiny, x); /*underflow*/ - k += 128; /* subnormal result */ - u.bits.exp = k; - return u.e*0x1p-128; + scale.e = 1.0L; + scale.bits.exp = 0x3fff + n; + return x * scale.e; } #endif