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Ulrich Drepper
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Jan 11, 2012
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Original file line number | Diff line number | Diff line change |
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/* | ||
* ==================================================== | ||
* 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" | ||
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static const double | ||
two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ | ||
twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ | ||
huge = 1.0e+300, | ||
tiny = 1.0e-300; | ||
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||
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 |
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