| 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 | <<trunc>>, <<truncf>>---round to integer, towards zero |
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| 14 | INDEX |
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| 15 | trunc |
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| 16 | INDEX |
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| 17 | truncf |
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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 trunc(double <[x]>); |
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| 22 | float truncf(float <[x]>); |
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| 23 | |
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| 24 | DESCRIPTION |
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| 25 | The <<trunc>> functions round their argument to the integer value, in |
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| 26 | floating format, nearest to but no larger in magnitude than the |
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| 27 | argument, regardless of the current rounding direction. (While the |
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| 28 | "inexact" floating-point exception behavior is unspecified by the C |
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| 29 | standard, the <<trunc>> functions are written so that "inexact" is not |
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| 30 | raised if the result does not equal the argument, which behavior is as |
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| 31 | recommended by IEEE 754 for its related functions.) |
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| 32 | |
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| 33 | RETURNS |
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| 34 | <[x]> truncated 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 | */ |
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| 40 | |
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| 41 | #include "fdlibm.h" |
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| 42 | |
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| 43 | #ifndef _DOUBLE_IS_32BITS |
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| 44 | |
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| 45 | #ifdef __STDC__ |
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| 46 | double trunc(double x) |
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| 47 | #else |
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| 48 | double trunc(x) |
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| 49 | double x; |
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| 50 | #endif |
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| 51 | { |
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| 52 | int signbit; |
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| 53 | /* Most significant word, least significant word. */ |
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| 54 | int msw; |
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| 55 | unsigned int lsw; |
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| 56 | int exponent_less_1023; |
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| 57 | |
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| 58 | EXTRACT_WORDS(msw, lsw, x); |
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| 59 | |
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| 60 | /* Extract sign bit. */ |
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| 61 | signbit = msw & 0x80000000; |
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| 62 | |
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| 63 | /* Extract exponent field. */ |
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| 64 | exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023; |
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| 65 | |
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| 66 | if (exponent_less_1023 < 20) |
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| 67 | { |
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| 68 | /* All significant digits are in msw. */ |
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| 69 | if (exponent_less_1023 < 0) |
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| 70 | { |
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| 71 | /* -1 < x < 1, so result is +0 or -0. */ |
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| 72 | INSERT_WORDS(x, signbit, 0); |
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| 73 | } |
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| 74 | else |
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| 75 | { |
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| 76 | /* All relevant fraction bits are in msw, so lsw of the result is 0. */ |
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| 77 | INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 0); |
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| 78 | } |
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| 79 | } |
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| 80 | else if (exponent_less_1023 > 51) |
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| 81 | { |
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| 82 | if (exponent_less_1023 == 1024) |
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| 83 | { |
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| 84 | /* x is infinite, or not a number, so trigger an exception. */ |
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| 85 | return x + x; |
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| 86 | } |
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| 87 | /* All bits in the fraction fields of the msw and lsw are needed in the result. */ |
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| 88 | } |
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| 89 | else |
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| 90 | { |
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| 91 | /* All fraction bits in msw are relevant. Truncate irrelevant |
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| 92 | bits from lsw. */ |
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| 93 | INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20))); |
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| 94 | } |
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| 95 | return x; |
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| 96 | } |
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| 97 | |
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| 98 | #endif /* _DOUBLE_IS_32BITS */ |
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