| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * ==================================================== |
| 3 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 4 | * |
| 5 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
| 6 | * Permission to use, copy, modify, and distribute this |
| 7 | * software is freely granted, provided that this notice |
| 8 | * is preserved. |
| 9 | * ==================================================== |
| 10 | */ |
| 11 | |
| 12 | /* |
| 13 | * rint(x) |
| 14 | * Return x rounded to integral value according to the prevailing |
| 15 | * rounding mode. |
| 16 | * Method: |
| 17 | * Using floating addition. |
| 18 | * Exception: |
| 19 | * Inexact flag raised if x not equal to rint(x). |
| 20 | */ |
| 21 | |
| 22 | #include "math.h" |
| 23 | #include "math_private.h" |
| 24 | |
| 25 | static const double |
| 26 | TWO52[2]={ |
| 27 | 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ |
| 28 | -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ |
| 29 | }; |
| 30 | |
| 31 | double rint(double x) |
| 32 | { |
| 33 | int32_t i0, j0, sx; |
| 34 | u_int32_t i,i1; |
| 35 | double t; |
| 36 | /* We use w = x + 2^52; t = w - 2^52; trick to round x to integer. |
| 37 | * This trick requires that compiler does not optimize it |
| 38 | * by keeping intermediate result w in a register wider than double. |
| 39 | * Declaring w volatile assures that value gets truncated to double |
| 40 | * (unfortunately, it also forces store+load): |
| 41 | */ |
| 42 | volatile double w; |
| 43 | |
| 44 | EXTRACT_WORDS(i0,i1,x); |
| 45 | /* Unbiased exponent */ |
| 46 | j0 = ((((u_int32_t)i0) >> 20)&0x7ff)-0x3ff; |
| 47 | |
| 48 | if (j0 > 51) { |
| 49 | //Why bother? Just returning x works too |
| 50 | //if (j0 == 0x400) /* inf or NaN */ |
| 51 | // return x+x; |
| 52 | return x; /* x is integral */ |
| 53 | } |
| 54 | |
| 55 | /* Sign */ |
| 56 | sx = ((u_int32_t)i0) >> 31; |
| 57 | |
| 58 | if (j0<20) { |
| 59 | if (j0<0) { /* |x| < 1 */ |
| 60 | if (((i0&0x7fffffff)|i1)==0) return x; |
| 61 | i1 |= (i0&0x0fffff); |
| 62 | i0 &= 0xfffe0000; |
| 63 | i0 |= ((i1|-i1)>>12)&0x80000; |
| 64 | SET_HIGH_WORD(x,i0); |
| 65 | w = TWO52[sx]+x; |
| 66 | t = w-TWO52[sx]; |
| 67 | GET_HIGH_WORD(i0,t); |
| 68 | SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31)); |
| 69 | return t; |
| 70 | } else { |
| 71 | i = (0x000fffff)>>j0; |
| 72 | if (((i0&i)|i1)==0) return x; /* x is integral */ |
| 73 | i>>=1; |
| 74 | if (((i0&i)|i1)!=0) { |
| 75 | if (j0==19) i1 = 0x40000000; |
| 76 | else i0 = (i0&(~i))|((0x20000)>>j0); |
| 77 | } |
| 78 | } |
| 79 | } else { |
| 80 | i = ((u_int32_t)(0xffffffff))>>(j0-20); |
| 81 | if ((i1&i)==0) return x; /* x is integral */ |
| 82 | i>>=1; |
| 83 | if ((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); |
| 84 | } |
| 85 | INSERT_WORDS(x,i0,i1); |
| 86 | w = TWO52[sx]+x; |
| 87 | return w-TWO52[sx]; |
| 88 | } |
| 89 | libm_hidden_def(rint) |
| 90 | |
| 91 | strong_alias(rint, nearbyint) |
| 92 | libm_hidden_def(nearbyint) |