source: trunk/minix/lib/float/mul_ext.c@ 10

Last change on this file since 10 was 9, checked in by Mattia Monga, 14 years ago

Minix 3.1.2a
File size: 2.3 KB
Line 
1/*
2 (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
3 See the copyright notice in the ACK home directory, in the file "Copyright".
4*/
5
6/* $Header: /cvsup/minix/src/lib/float/mul_ext.c,v 1.1.1.1 2005/04/21 14:56:11 beng Exp $ */
7
8/*
9 ROUTINE TO MULTIPLY TWO EXTENDED FORMAT NUMBERS
10*/
11
12# include "FP_bias.h"
13# include "FP_trap.h"
14# include "FP_types.h"
15# include "FP_shift.h"
16
17void
18mul_ext(e1,e2)
19EXTEND *e1,*e2;
20{
21 register int i,j; /* loop control */
22 unsigned short mp[4]; /* multiplier */
23 unsigned short mc[4]; /* multipcand */
24 unsigned short result[8]; /* result */
25 register unsigned short *pres;
26
27 /* first save the sign (XOR) */
28 e1->sign ^= e2->sign;
29
30 /* compute new exponent */
31 e1->exp += e2->exp + 1;
32 /* 128 bit multiply of mantissas */
33
34 /* assign unknown long formats */
35 /* to known unsigned word formats */
36 mp[0] = e1->m1 >> 16;
37 mp[1] = (unsigned short) e1->m1;
38 mp[2] = e1->m2 >> 16;
39 mp[3] = (unsigned short) e1->m2;
40 mc[0] = e2->m1 >> 16;
41 mc[1] = (unsigned short) e2->m1;
42 mc[2] = e2->m2 >> 16;
43 mc[3] = (unsigned short) e2->m2;
44 for (i = 8; i--;) {
45 result[i] = 0;
46 }
47 /*
48 * fill registers with their components
49 */
50 for(i=4, pres = &result[4];i--;pres--) if (mp[i]) {
51 unsigned short k = 0;
52 unsigned long mpi = mp[i];
53 for(j=4;j--;) {
54 unsigned long tmp = (unsigned long)pres[j] + k;
55 if (mc[j]) tmp += mpi * mc[j];
56 pres[j] = tmp;
57 k = tmp >> 16;
58 }
59 pres[-1] = k;
60 }
61 if (! (result[0] & 0x8000)) {
62 e1->exp--;
63 for (i = 0; i <= 3; i++) {
64 result[i] <<= 1;
65 if (result[i+1]&0x8000) result[i] |= 1;
66 }
67 result[4] <<= 1;
68 }
69
70 /*
71 * combine the registers to a total
72 */
73 e1->m1 = ((unsigned long)(result[0]) << 16) + result[1];
74 e1->m2 = ((unsigned long)(result[2]) << 16) + result[3];
75 if (result[4] & 0x8000) {
76 if (++e1->m2 == 0)
77 if (++e1->m1 == 0) {
78 e1->m1 = NORMBIT;
79 e1->exp++;
80 }
81 }
82
83 /* check for overflow */
84 if (e1->exp >= EXT_MAX) {
85 trap(EFOVFL);
86 /* if caught */
87 /* return signed infinity */
88 e1->exp = EXT_MAX;
89infinity: e1->m1 = e1->m2 =0L;
90 return;
91 }
92 /* check for underflow */
93 if (e1->exp < EXT_MIN) {
94 trap(EFUNFL);
95 e1->exp = EXT_MIN;
96 goto infinity;
97 }
98}
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