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4349 | Serge | 1 | /* |
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 | < |
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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 | |||
19 | ANSI_SYNOPSIS |
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20 | #include |
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21 | double trunc(double <[x]>); |
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22 | float truncf(float <[x]>); |
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23 | |||
24 | DESCRIPTION |
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25 | The < |
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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 < |
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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 | |||
33 | RETURNS |
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34 | <[x]> truncated to an integral value. |
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35 | |||
36 | PORTABILITY |
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37 | ANSI C, POSIX |
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38 | |||
39 | */ |
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40 | |||
41 | #include "fdlibm.h" |
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42 | |||
43 | #ifndef _DOUBLE_IS_32BITS |
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44 | |||
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 | |||
58 | EXTRACT_WORDS(msw, lsw, x); |
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59 | |||
60 | /* Extract sign bit. */ |
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61 | signbit = msw & 0x80000000; |
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62 | |||
63 | /* Extract exponent field. */ |
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64 | exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023; |
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65 | |||
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 | |||
98 | #endif /* _DOUBLE_IS_32BITS */>>>>[x]> |