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| 2 | /* @(#)s_scalbn.c 5.1 93/09/24 */
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| 3 | /*
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| 4 | * ====================================================
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| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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| 6 | *
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| 7 | * Developed at SunPro, a Sun Microsystems, Inc. business.
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| 8 | * Permission to use, copy, modify, and distribute this
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| 9 | * software is freely granted, provided that this notice
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| 10 | * is preserved.
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| 11 | * ====================================================
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| 12 | */
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| 13 |
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| 14 | /*
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| 15 | FUNCTION
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| 16 | <<scalbn>>, <<scalbnf>>---scale by integer
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| 17 | INDEX
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| 18 | scalbn
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| 19 | INDEX
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| 20 | scalbnf
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| 21 |
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| 22 | ANSI_SYNOPSIS
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| 23 | #include <math.h>
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| 24 | double scalbn(double <[x]>, int <[y]>);
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| 25 | float scalbnf(float <[x]>, int <[y]>);
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| 26 |
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| 27 | TRAD_SYNOPSIS
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| 28 | #include <math.h>
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| 29 | double scalbn(<[x]>,<[y]>)
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| 30 | double <[x]>;
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| 31 | int <[y]>;
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| 32 | float scalbnf(<[x]>,<[y]>)
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| 33 | float <[x]>;
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| 34 | int <[y]>;
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| 35 |
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| 36 | DESCRIPTION
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| 37 | <<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times
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| 38 | 2 to the power <[n]>. The result is computed by manipulating the
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| 39 | exponent, rather than by actually performing an exponentiation or
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| 40 | multiplication.
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| 41 |
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| 42 | RETURNS
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| 43 | <[x]> times 2 to the power <[n]>.
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| 44 |
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| 45 | PORTABILITY
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| 46 | Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V
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| 47 | Interface Definition (Issue 2).
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| 48 |
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| 49 | */
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| 50 |
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| 51 | /*
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| 52 | * scalbn (double x, int n)
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| 53 | * scalbn(x,n) returns x* 2**n computed by exponent
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| 54 | * manipulation rather than by actually performing an
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| 55 | * exponentiation or a multiplication.
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| 56 | */
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| 57 |
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| 58 | #include "fdlibm.h"
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| 59 |
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| 60 | #ifndef _DOUBLE_IS_32BITS
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| 61 |
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| 62 | #ifdef __STDC__
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| 63 | static const double
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| 64 | #else
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| 65 | static double
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| 66 | #endif
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| 67 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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| 68 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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| 69 | huge = 1.0e+300,
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| 70 | tiny = 1.0e-300;
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| 71 |
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| 72 | #ifdef __STDC__
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| 73 | double scalbn (double x, int n)
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| 74 | #else
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| 75 | double scalbn (x,n)
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| 76 | double x; int n;
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| 77 | #endif
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| 78 | {
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| 79 | int32_t k,hx,lx;
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| 80 | EXTRACT_WORDS(hx,lx,x);
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| 81 | k = (hx&0x7ff00000)>>20; /* extract exponent */
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| 82 | if (k==0) { /* 0 or subnormal x */
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| 83 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
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| 84 | x *= two54;
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| 85 | GET_HIGH_WORD(hx,x);
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| 86 | k = ((hx&0x7ff00000)>>20) - 54;
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| 87 | if (n< -50000) return tiny*x; /*underflow*/
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| 88 | }
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| 89 | if (k==0x7ff) return x+x; /* NaN or Inf */
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| 90 | k = k+n;
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| 91 | if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
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| 92 | if (k > 0) /* normal result */
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| 93 | {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
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| 94 | if (k <= -54) {
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| 95 | if (n > 50000) /* in case integer overflow in n+k */
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| 96 | return huge*copysign(huge,x); /*overflow*/
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| 97 | else return tiny*copysign(tiny,x); /*underflow*/
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| 98 | }
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| 99 | k += 54; /* subnormal result */
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| 100 | SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
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| 101 | return x*twom54;
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| 102 | }
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| 103 |
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| 104 | #endif /* _DOUBLE_IS_32BITS */
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