| 1 | /* sf_cbrt.c -- float version of s_cbrt.c. |
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| 2 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
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| 3 | */ |
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| 4 | |
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| 5 | /* |
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| 6 | * ==================================================== |
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| 7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 8 | * |
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| 9 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 10 | * Permission to use, copy, modify, and distribute this |
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| 11 | * software is freely granted, provided that this notice |
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| 12 | * is preserved. |
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| 13 | * ==================================================== |
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| 14 | * |
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| 15 | */ |
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| 16 | |
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| 17 | #include "fdlibm.h" |
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| 18 | |
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| 19 | /* cbrtf(x) |
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| 20 | * Return cube root of x |
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| 21 | */ |
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| 22 | #ifdef __STDC__ |
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| 23 | static const __uint32_t |
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| 24 | #else |
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| 25 | static __uint32_t |
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| 26 | #endif |
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| 27 | B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */ |
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| 28 | B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */ |
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| 29 | |
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| 30 | #ifdef __STDC__ |
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| 31 | static const float |
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| 32 | #else |
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| 33 | static float |
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| 34 | #endif |
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| 35 | C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */ |
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| 36 | D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */ |
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| 37 | E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */ |
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| 38 | F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */ |
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| 39 | G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */ |
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| 40 | |
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| 41 | #ifdef __STDC__ |
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| 42 | float cbrtf(float x) |
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| 43 | #else |
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| 44 | float cbrtf(x) |
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| 45 | float x; |
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| 46 | #endif |
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| 47 | { |
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| 48 | __int32_t hx; |
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| 49 | float r,s,t; |
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| 50 | __uint32_t sign; |
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| 51 | __uint32_t high; |
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| 52 | |
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| 53 | GET_FLOAT_WORD(hx,x); |
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| 54 | sign=hx&0x80000000; /* sign= sign(x) */ |
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| 55 | hx ^=sign; |
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| 56 | if(!FLT_UWORD_IS_FINITE(hx)) |
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| 57 | return(x+x); /* cbrt(NaN,INF) is itself */ |
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| 58 | if(FLT_UWORD_IS_ZERO(hx)) |
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| 59 | return(x); /* cbrt(0) is itself */ |
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| 60 | |
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| 61 | SET_FLOAT_WORD(x,hx); /* x <- |x| */ |
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| 62 | /* rough cbrt to 5 bits */ |
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| 63 | if(FLT_UWORD_IS_SUBNORMAL(hx)) /* subnormal number */ |
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| 64 | {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */ |
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| 65 | t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2); |
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| 66 | } |
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| 67 | else |
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| 68 | SET_FLOAT_WORD(t,hx/3+B1); |
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| 69 | |
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| 70 | |
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| 71 | /* new cbrt to 23 bits */ |
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| 72 | r=t*t/x; |
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| 73 | s=C+r*t; |
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| 74 | t*=G+F/(s+E+D/s); |
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| 75 | |
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| 76 | /* retore the sign bit */ |
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| 77 | GET_FLOAT_WORD(high,t); |
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| 78 | SET_FLOAT_WORD(t,high|sign); |
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| 79 | return(t); |
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| 80 | } |
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| 81 | |
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| 82 | #ifdef _DOUBLE_IS_32BITS |
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| 83 | |
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| 84 | #ifdef __STDC__ |
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| 85 | double cbrt(double x) |
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| 86 | #else |
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| 87 | double cbrt(x) |
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| 88 | double x; |
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| 89 | #endif |
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| 90 | { |
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| 91 | return (double) cbrtf((float) x); |
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| 92 | } |
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| 93 | |
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| 94 | #endif /* defined(_DOUBLE_IS_32BITS) */ |
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