| 1 | /* |
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| 2 | * ==================================================== |
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| 3 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 4 | * |
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| 5 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 6 | * Permission to use, copy, modify, and distribute this |
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| 7 | * software is freely granted, provided that this notice |
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| 8 | * is preserved. |
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| 9 | * ==================================================== |
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| 10 | */ |
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| 11 | /* |
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| 12 | FUNCTION |
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| 13 | <<round>>, <<roundf>>---round to integer, to nearest |
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| 14 | INDEX |
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| 15 | round |
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| 16 | INDEX |
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| 17 | roundf |
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| 18 | |
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| 19 | SYNOPSIS |
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| 20 | #include <math.h> |
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| 21 | double round(double <[x]>); |
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| 22 | float roundf(float <[x]>); |
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| 23 | |
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| 24 | DESCRIPTION |
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| 25 | The <<round>> functions round their argument to the nearest integer |
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| 26 | value in floating-point format, rounding halfway cases away from zero, |
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| 27 | regardless of the current rounding direction. (While the "inexact" |
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| 28 | floating-point exception behavior is unspecified by the C standard, the |
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| 29 | <<round>> functions are written so that "inexact" is not raised if the |
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| 30 | result does not equal the argument, which behavior is as recommended by |
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| 31 | IEEE 754 for its related functions.) |
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| 32 | |
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| 33 | RETURNS |
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| 34 | <[x]> rounded to an integral value. |
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| 35 | |
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| 36 | PORTABILITY |
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| 37 | ANSI C, POSIX |
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| 38 | |
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| 39 | SEEALSO |
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| 40 | <<nearbyint>>, <<rint>> |
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| 41 | |
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| 42 | */ |
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| 43 | |
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| 44 | #include "fdlibm.h" |
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| 45 | |
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| 46 | #ifndef _DOUBLE_IS_32BITS |
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| 47 | |
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| 48 | #ifdef __STDC__ |
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| 49 | double round(double x) |
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| 50 | #else |
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| 51 | double round(x) |
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| 52 | double x; |
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| 53 | #endif |
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| 54 | { |
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| 55 | /* Most significant word, least significant word. */ |
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| 56 | __int32_t msw, exponent_less_1023; |
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| 57 | __uint32_t lsw; |
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| 58 | |
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| 59 | EXTRACT_WORDS(msw, lsw, x); |
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| 60 | |
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| 61 | /* Extract exponent field. */ |
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| 62 | exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023; |
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| 63 | |
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| 64 | if (exponent_less_1023 < 20) |
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| 65 | { |
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| 66 | if (exponent_less_1023 < 0) |
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| 67 | { |
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| 68 | msw &= 0x80000000; |
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| 69 | if (exponent_less_1023 == -1) |
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| 70 | /* Result is +1.0 or -1.0. */ |
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| 71 | msw |= (1023 << 20); |
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| 72 | lsw = 0; |
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| 73 | } |
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| 74 | else |
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| 75 | { |
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| 76 | __uint32_t exponent_mask = 0x000fffff >> exponent_less_1023; |
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| 77 | if ((msw & exponent_mask) == 0 && lsw == 0) |
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| 78 | /* x in an integral value. */ |
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| 79 | return x; |
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| 80 | |
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| 81 | msw += 0x00080000 >> exponent_less_1023; |
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| 82 | msw &= ~exponent_mask; |
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| 83 | lsw = 0; |
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| 84 | } |
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| 85 | } |
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| 86 | else if (exponent_less_1023 > 51) |
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| 87 | { |
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| 88 | if (exponent_less_1023 == 1024) |
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| 89 | /* x is NaN or infinite. */ |
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| 90 | return x + x; |
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| 91 | else |
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| 92 | return x; |
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| 93 | } |
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| 94 | else |
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| 95 | { |
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| 96 | __uint32_t exponent_mask = 0xffffffff >> (exponent_less_1023 - 20); |
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| 97 | __uint32_t tmp; |
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| 98 | |
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| 99 | if ((lsw & exponent_mask) == 0) |
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| 100 | /* x is an integral value. */ |
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| 101 | return x; |
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| 102 | |
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| 103 | tmp = lsw + (1 << (51 - exponent_less_1023)); |
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| 104 | if (tmp < lsw) |
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| 105 | msw += 1; |
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| 106 | lsw = tmp; |
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| 107 | |
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| 108 | lsw &= ~exponent_mask; |
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| 109 | } |
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| 110 | INSERT_WORDS(x, msw, lsw); |
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| 111 | |
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| 112 | return x; |
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| 113 | } |
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| 114 | |
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| 115 | #endif /* _DOUBLE_IS_32BITS */ |
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