| 1 | /* @(#)s_scalbn.c 5.1 93/09/24 */ |
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| 2 | /* |
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| 3 | * ==================================================== |
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| 4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 5 | * |
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| 6 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 7 | * Permission to use, copy, modify, and distribute this |
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| 8 | * software is freely granted, provided that this notice |
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| 9 | * is preserved. |
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| 10 | * ==================================================== |
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| 11 | */ |
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| 12 | |
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| 13 | /* |
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| 14 | * scalbn (double x, int n) |
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| 15 | * scalbn(x,n) returns x* 2**n computed by exponent |
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| 16 | * manipulation rather than by actually performing an |
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| 17 | * exponentiation or a multiplication. |
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| 18 | */ |
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| 19 | |
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| 20 | #include "fdlibm.h" |
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| 21 | |
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| 22 | #ifndef _DOUBLE_IS_32BITS |
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| 23 | |
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| 24 | #ifdef __STDC__ |
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| 25 | static const double |
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| 26 | #else |
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| 27 | static double |
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| 28 | #endif |
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| 29 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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| 30 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
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| 31 | huge = 1.0e+300, |
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| 32 | tiny = 1.0e-300; |
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| 33 | |
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| 34 | #ifdef __STDC__ |
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| 35 | double scalbln (double x, long int n) |
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| 36 | #else |
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| 37 | double scalbln (x,n) |
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| 38 | double x; long int n; |
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| 39 | #endif |
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| 40 | { |
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| 41 | __int32_t k,hx,lx; |
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| 42 | EXTRACT_WORDS(hx,lx,x); |
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| 43 | k = (hx&0x7ff00000)>>20; /* extract exponent */ |
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| 44 | if (k==0) { /* 0 or subnormal x */ |
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| 45 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
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| 46 | x *= two54; |
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| 47 | GET_HIGH_WORD(hx,x); |
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| 48 | k = ((hx&0x7ff00000)>>20) - 54; |
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| 49 | } |
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| 50 | if (k==0x7ff) return x+x; /* NaN or Inf */ |
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| 51 | k = k+n; |
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| 52 | if (n> 50000 || k > 0x7fe) |
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| 53 | return huge*copysign(huge,x); /* overflow */ |
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| 54 | if (n< -50000) return tiny*copysign(tiny,x); /*underflow*/ |
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| 55 | if (k > 0) /* normal result */ |
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| 56 | {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} |
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| 57 | if (k <= -54) |
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| 58 | return tiny*copysign(tiny,x); /*underflow*/ |
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| 59 | k += 54; /* subnormal result */ |
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| 60 | SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); |
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| 61 | return x*twom54; |
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| 62 | } |
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| 63 | |
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| 64 | #endif /* _DOUBLE_IS_32BITS */ |
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