120 lines
3.1 KiB
C
120 lines
3.1 KiB
C
/*
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(c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
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See the copyright notice in the ACK home directory, in the file "Copyright".
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*/
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/* $Header$ */
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/*
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ROUTINE TO MULTIPLY TWO EXTENDED FORMAT NUMBERS
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*/
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# include "adder.h"
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# include "FP_bias.h"
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# include "FP_trap.h"
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# include "FP_types.h"
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mul_ext(e1,e2)
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EXTEND *e1,*e2;
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{
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register int i,j; /* loop control */
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short unsigned mp[4]; /* multiplier */
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short unsigned mc[4]; /* multipcand */
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short unsigned result[8]; /* result */
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B64 tmp64;
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register unsigned short *pres;
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/* first save the sign (XOR) */
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e1->sign ^= e2->sign;
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/********************************************************/
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/* INCREASE EXPONENT BY ONE (1) */
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/* */
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/* the nature of the multiplication algorithm used */
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/* results in an exponent that is small by an additive */
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/* factor of one (1); */
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/* if the maximum bit is set it will not be subtracted */
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/* during normalization -> this is correct and can be */
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/* expected often with normalized numbers */
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/* HOWEVER, it is also possible that unnormalized */
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/* numbers are used. Rather than shifting here */
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/* always(!) (unless L bit is set) I chose to */
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/* increase the exponent by one - a simple (FAST) */
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/* process - and to decrease it later during */
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/* normalization. */
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/* */
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/********************************************************/
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/* The effects of bias (as used here) */
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/* and the multiplication algorithm used cancel */
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/* so these statements are commented out */
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/* August 1985 - if changing the Leading Bit (or NORMBIT) */
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/* this problem with the multiplication algorithm no longer */
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/* exists - bias must be subtracted now */
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/* */
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/* e1->exp++; */
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/********************************************************/
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/* next add the exponents */
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e1->exp += e2->exp;
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e1->exp -= 1; /* correction for bias */
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/* check for overflow */
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if (e1->exp >= EXT_MAX) {
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trap(EFOVFL);
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/* if caught */
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/* return signed infinity */
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e1->exp = EXT_MAX;
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infinity: e1->m1 = e1->m2 =0L;
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return;
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}
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/* check for underflow */
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if (e1->exp < EXT_MIN) {
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trap(EFUNFL);
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e1->exp = EXT_MIN;
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goto infinity;
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}
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/* 128 bit multiply of mantissas */
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/* assign unknown long formats */
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/* to known unsigned word formats */
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mp[0] = e1->m1 >> 16;
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mp[1] = (unsigned short) e1->m1;
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mp[2] = e1->m2 >> 16;
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mp[3] = (unsigned short) e1->m2;
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mc[0] = e2->m1 >> 16;
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mc[1] = (unsigned short) e2->m1;
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mc[2] = e2->m2 >> 16;
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mc[3] = (unsigned short) e2->m2;
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for (i = 8; i--;) {
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result[i] = 0;
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}
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/*
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* fill registers with their components
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*/
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for(i=4, pres = &result[4];i--;pres--) if (mp[i]) {
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unsigned short k = 0;
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unsigned long mpi = mp[i];
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for(j=4;j--;) {
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unsigned long tmp = (unsigned long)pres[j] + k;
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if (mc[j]) tmp += mpi * mc[j];
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pres[j] = tmp;
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k = tmp >> 16;
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}
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pres[-1] = k;
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}
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/*
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* combine the registers to a total
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*/
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e1->m1 = ((unsigned long)(result[0]) << 16) + result[1];
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e1->m2 = ((unsigned long)(result[2]) << 16) + result[3];
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if (result[4] & 0x8000) {
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if (++e1->m2 == 0)
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e1->m1++;
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}
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nrm_ext(e1);
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}
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