/* flonum_mult.c - multiply two flonums | |

Copyright (C) 1987-2021 Free Software Foundation, Inc. | |

This file is part of GAS, the GNU Assembler. | |

GAS is free software; you can redistribute it and/or modify | |

it under the terms of the GNU General Public License as published by | |

the Free Software Foundation; either version 3, or (at your option) | |

any later version. | |

GAS is distributed in the hope that it will be useful, but WITHOUT | |

ANY WARRANTY; without even the implied warranty of MERCHANTABILITY | |

or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public | |

License for more details. | |

You should have received a copy of the GNU General Public License | |

along with GAS; see the file COPYING. If not, write to the Free | |

Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA | |

02110-1301, USA. */ | |

#include "ansidecl.h" | |

#include "flonum.h" | |

/* plan for a . b => p(roduct) | |

+-------+-------+-/ /-+-------+-------+ | |

| a | a | ... | a | a | | |

| A | A-1 | | 1 | 0 | | |

+-------+-------+-/ /-+-------+-------+ | |

+-------+-------+-/ /-+-------+-------+ | |

| b | b | ... | b | b | | |

| B | B-1 | | 1 | 0 | | |

+-------+-------+-/ /-+-------+-------+ | |

+-------+-------+-/ /-+-------+-/ /-+-------+-------+ | |

| p | p | ... | p | ... | p | p | | |

| A+B+1| A+B | | N | | 1 | 0 | | |

+-------+-------+-/ /-+-------+-/ /-+-------+-------+ | |

/^\ | |

(carry) a .b ... | ... a .b a .b | |

A B | 0 1 0 0 | |

| | |

... | ... a .b | |

| 1 0 | |

| | |

| ... | |

| | |

| | |

| | |

| ___ | |

| \ | |

+----- P = > a .b | |

N /__ i j | |

N = 0 ... A+B | |

for all i,j where i+j=N | |

[i,j integers > 0] | |

a[], b[], p[] may not intersect. | |

Zero length factors signify 0 significant bits: treat as 0.0. | |

0.0 factors do the right thing. | |

Zero length product OK. | |

I chose the ForTran accent "foo[bar]" instead of the C accent "*garply" | |

because I felt the ForTran way was more intuitive. The C way would | |

probably yield better code on most C compilers. Dean Elsner. | |

(C style also gives deeper insight [to me] ... oh well ...) */ | |

void | |

flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b, | |

FLONUM_TYPE *product) | |

{ | |

int size_of_a; /* 0 origin */ | |

int size_of_b; /* 0 origin */ | |

int size_of_product; /* 0 origin */ | |

int size_of_sum; /* 0 origin */ | |

int extra_product_positions; /* 1 origin */ | |

unsigned long work; | |

unsigned long carry; | |

long exponent; | |

LITTLENUM_TYPE *q; | |

long significant; /* TRUE when we emit a non-0 littlenum */ | |

/* ForTran accent follows. */ | |

int P; /* Scan product low-order -> high. */ | |

int N; /* As in sum above. */ | |

int A; /* Which [] of a? */ | |

int B; /* Which [] of b? */ | |

if ((a->sign != '-' && a->sign != '+') | |

|| (b->sign != '-' && b->sign != '+')) | |

{ | |

/* Got to fail somehow. Any suggestions? */ | |

product->sign = 0; | |

return; | |

} | |

product->sign = (a->sign == b->sign) ? '+' : '-'; | |

size_of_a = a->leader - a->low; | |

size_of_b = b->leader - b->low; | |

exponent = a->exponent + b->exponent; | |

size_of_product = product->high - product->low; | |

size_of_sum = size_of_a + size_of_b; | |

extra_product_positions = size_of_product - size_of_sum; | |

if (extra_product_positions < 0) | |

{ | |

P = extra_product_positions; /* P < 0 */ | |

exponent -= extra_product_positions; /* Increases exponent. */ | |

} | |

else | |

{ | |

P = 0; | |

} | |

carry = 0; | |

significant = 0; | |

for (N = 0; N <= size_of_sum; N++) | |

{ | |

work = carry; | |

carry = 0; | |

for (A = 0; A <= N; A++) | |

{ | |

B = N - A; | |

if (A <= size_of_a && B <= size_of_b && B >= 0) | |

{ | |

#ifdef TRACE | |

printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n", | |

A, a->low[A], B, b->low[B], work); | |

#endif | |

/* Watch out for sign extension! Without the casts, on | |

the DEC Alpha, the multiplication result is *signed* | |

int, which gets sign-extended to convert to the | |

unsigned long! */ | |

work += (unsigned long) a->low[A] * (unsigned long) b->low[B]; | |

carry += work >> LITTLENUM_NUMBER_OF_BITS; | |

work &= LITTLENUM_MASK; | |

#ifdef TRACE | |

printf ("work=%08x carry=%04x\n", work, carry); | |

#endif | |

} | |

} | |

significant |= work; | |

if (significant || P < 0) | |

{ | |

if (P >= 0) | |

{ | |

product->low[P] = work; | |

#ifdef TRACE | |

printf ("P=%d. work[p]:=%04x\n", P, work); | |

#endif | |

} | |

P++; | |

} | |

else | |

{ | |

extra_product_positions++; | |

exponent++; | |

} | |

} | |

/* [P]-> position # size_of_sum + 1. | |

This is where 'carry' should go. */ | |

#ifdef TRACE | |

printf ("final carry =%04x\n", carry); | |

#endif | |

if (carry) | |

{ | |

if (extra_product_positions > 0) | |

product->low[P] = carry; | |

else | |

{ | |

/* No room at high order for carry littlenum. */ | |

/* Shift right 1 to make room for most significant littlenum. */ | |

exponent++; | |

P--; | |

for (q = product->low + P; q >= product->low; q--) | |

{ | |

work = *q; | |

*q = carry; | |

carry = work; | |

} | |

} | |

} | |

else | |

P--; | |

product->leader = product->low + P; | |

product->exponent = exponent; | |

} |