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author | Ulrich Drepper <drepper@gmail.com> | 2012-01-11 12:49:16 -0500 |
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committer | Ulrich Drepper <drepper@gmail.com> | 2012-01-11 12:49:16 -0500 |
commit | 41d0e8696f370d625390da356d95cab174c7990e (patch) | |
tree | 545ebdab16006b67c7a2156f8c5f7d0ceee139e1 /sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c | |
parent | 5452bffeefe076a12eeb04f784ef1209a4282038 (diff) | |
download | glibc-41d0e8696f370d625390da356d95cab174c7990e.tar.gz glibc-41d0e8696f370d625390da356d95cab174c7990e.tar.xz glibc-41d0e8696f370d625390da356d95cab174c7990e.zip |
Optimize scalbln
Diffstat (limited to 'sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c')
-rw-r--r-- | sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c new file mode 100644 index 0000000000..d6b97b5483 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c @@ -0,0 +1,60 @@ +/* + * ==================================================== + * 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 "math.h" +#include "math_private.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 +__scalbln (double x, long int n) +{ + int64_t ix; + int64_t k; + EXTRACT_WORDS64(ix,x); + k = (ix >> 52) & 0x7ff; /* extract exponent */ + if (__builtin_expect(k==0, 0)) { /* 0 or subnormal x */ + if ((ix & UINT64_C(0xfffffffffffff))==0) return x; /* +-0 */ + x *= two54; + EXTRACT_WORDS64(ix,x); + k = ((ix >> 52) & 0x7ff) - 54; + } + if (__builtin_expect(k==0x7ff, 0)) return x+x; /* NaN or Inf */ + k = k+n; + if (__builtin_expect(n> 50000 || k > 0x7fe, 0)) + return huge*__copysign(huge,x); /* overflow */ + if (__builtin_expect(n< -50000, 0)) + return tiny*__copysign(tiny,x); /*underflow*/ + if (__builtin_expect(k > 0, 1)) /* normal result */ + {INSERT_WORDS64(x,(ix&UINT64_C(0x800fffffffffffff))|(k<<52)); + return x;} + if (k <= -54) + return tiny*__copysign(tiny,x); /*underflow*/ + k += 54; /* subnormal result */ + INSERT_WORDS64(x,(ix&INT64_C(0x800fffffffffffff))|(k<<52)); + return x*twom54; +} +weak_alias (__scalbln, scalbln) +#ifdef NO_LONG_DOUBLE +strong_alias (__scalbln, __scalblnl) +weak_alias (__scalbln, scalblnl) +#endif |