1/* $NetBSD: fixunsgen_ieee754.c,v 1.1 2011/07/09 02:30:27 matt Exp $ */ 2 3/*- 4 * Copyright (c) 1992, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This software was developed by the Computer Systems Engineering group 8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 9 * contributed to Berkeley. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 */ 35 36#include <sys/cdefs.h> 37 38#if !defined(FIXUNSNAME) && defined(LIBC_SCCS) && !defined(lint) 39__RCSID("$NetBSD: fixunsgen_ieee754.c,v 1.1 2011/07/09 02:30:27 matt Exp $"); 40#endif /* LIBC_SCCS and not lint */ 41 42#include <stddef.h> 43#include <stdint.h> 44#include <stdbool.h> 45#include <float.h> 46 47#ifndef FIXUNSNAME 48#define FIXUNSNAME(n) n##32 49#define UINTXX_T uint32_t 50#endif 51 52__dso_hidden UINTXX_T 53 FIXUNSNAME(__fixunsgen)(int, bool, size_t, size_t, const uint32_t *); 54 55/* 56 * Convert double to (unsigned) int. All operations are done module 2^32. 57 */ 58UINTXX_T 59FIXUNSNAME(__fixunsgen)(int exp, bool sign, size_t mant_dig, size_t fracbits, 60 const uint32_t *frac) 61{ 62 UINTXX_T tmp; 63 64 /* 65 * If it's less than 1 (negative exponent), it's going to round 66 * to zero. If the exponent is so large that it is a multiple of 67 * 2^N, then x module 2^N will be 0. (we use the fact treating a 68 * negative value as unsigned will be greater than nonnegative value) 69 */ 70 if (__predict_false((size_t)exp >= mant_dig + sizeof(UINTXX_T)*8)) 71 return 0; 72 73 /* 74 * This is simplier than it seems. Basically we are constructing 75 * fixed binary representation of the floating point number tossing 76 * away bits that wont be in the modulis we return. 77 */ 78 tmp = 1; 79 for (size_t ebits = exp;;) { 80 if (ebits <= fracbits) { 81 /* 82 * The current fraction has more bits than we need. 83 * Shift the current value over and insert the bits 84 * we want. We're done. 85 */ 86 tmp <<= ebits; 87 tmp |= *frac >> (fracbits - ebits); 88 break; 89 } 90 if (fracbits == sizeof(tmp)*4) { 91 /* 92 * Shifts must be < sizeof(type). If it's going to be 93 * sizeof(type), just replace the value. 94 */ 95 tmp = *frac--; 96 } else { 97 tmp <<= fracbits; 98 tmp |= *frac--; 99 } 100 ebits -= fracbits; 101 fracbits = sizeof(frac[0]) * 4; 102 } 103 104 /* 105 * If the input was negative, make tmp negative module 2^32. 106 */ 107 if (sign) 108 tmp = -tmp; 109 110 return tmp; 111} 112