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| Rev | Author | Line No. | Line |
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| 2 | pj | 1 | /* @(#)s_scalbn.c 5.1 93/09/24 */ |
| 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 | |||
| 13 | #ifndef lint |
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| 14 | static char rcsid[] = "$\Id: s_scalbn.c,v 1.2.6.1 1997/02/23 11:03:21 joerg Exp $"; |
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| 15 | #endif |
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| 16 | |||
| 17 | /* |
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| 18 | * scalbn (double x, int n) |
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| 19 | * scalbn(x,n) returns x* 2**n computed by exponent |
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| 20 | * manipulation rather than by actually performing an |
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| 21 | * exponentiation or a multiplication. |
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| 22 | */ |
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| 23 | |||
| 24 | #include "math.h" |
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| 25 | #include "math_private.h" |
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| 26 | |||
| 27 | #ifdef __STDC__ |
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| 28 | static const double |
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| 29 | #else |
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| 30 | static double |
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| 31 | #endif |
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| 32 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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| 33 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
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| 34 | huge = 1.0e+300, |
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| 35 | tiny = 1.0e-300; |
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| 36 | |||
| 37 | #ifdef __STDC__ |
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| 38 | double __generic_scalbn (double x, int n) |
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| 39 | #else |
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| 40 | double __generic_scalbn (x,n) |
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| 41 | double x; int n; |
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| 42 | #endif |
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| 43 | { |
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| 44 | int32_t k,hx,lx; |
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| 45 | EXTRACT_WORDS(hx,lx,x); |
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| 46 | k = (hx&0x7ff00000)>>20; /* extract exponent */ |
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| 47 | if (k==0) { /* 0 or subnormal x */ |
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| 48 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
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| 49 | x *= two54; |
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| 50 | GET_HIGH_WORD(hx,x); |
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| 51 | k = ((hx&0x7ff00000)>>20) - 54; |
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| 52 | if (n< -50000) return tiny*x; /*underflow*/ |
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| 53 | } |
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| 54 | if (k==0x7ff) return x+x; /* NaN or Inf */ |
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| 55 | k = k+n; |
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| 56 | if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ |
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| 57 | if (k > 0) /* normal result */ |
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| 58 | {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} |
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| 59 | if (k <= -54) |
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| 60 | if (n > 50000) /* in case integer overflow in n+k */ |
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| 61 | return huge*copysign(huge,x); /*overflow*/ |
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| 62 | else return tiny*copysign(tiny,x); /*underflow*/ |
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| 63 | k += 54; /* subnormal result */ |
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| 64 | SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); |
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| 65 | return x*twom54; |
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| 66 | } |