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fixunsgen_ieee754.c revision 1.2.2.1 
      1 /*	$NetBSD: fixunsgen_ieee754.c,v 1.2.2.1 2012/04/17 00:05:18 yamt 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 1.2.2.1 2012/04/17 00:05:18 yamt 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  */
     58 UINTXX_T
     59 FIXUNSNAME(__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 <<= (unsigned int)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 <<= (unsigned int)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