xref: /onnv-gate/usr/src/lib/libc/i386/gen/_mul64.s (revision 7298:b69e27387f74)
10Sstevel@tonic-gate/*
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70Sstevel@tonic-gate *
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200Sstevel@tonic-gate */
210Sstevel@tonic-gate/*
220Sstevel@tonic-gate * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
230Sstevel@tonic-gate * Use is subject to license terms.
240Sstevel@tonic-gate */
250Sstevel@tonic-gate
26*7298SMark.J.Nelson@Sun.COM	.file	"_mul64.s"
270Sstevel@tonic-gate
280Sstevel@tonic-gate/
290Sstevel@tonic-gate/   function __mul64(A,B:Longint):Longint;
300Sstevel@tonic-gate/	{Overflow is not checked}
310Sstevel@tonic-gate/
320Sstevel@tonic-gate/ We essentially do multiply by longhand, using base 2**32 digits.
330Sstevel@tonic-gate/               a       b	parameter A
340Sstevel@tonic-gate/	     x 	c       d	parameter B
350Sstevel@tonic-gate/		---------
360Sstevel@tonic-gate/               ad      bd
370Sstevel@tonic-gate/       ac	bc
380Sstevel@tonic-gate/       -----------------
390Sstevel@tonic-gate/       ac	ad+bc	bd
400Sstevel@tonic-gate/
410Sstevel@tonic-gate/       We can ignore ac and top 32 bits of ad+bc: if <> 0, overflow happened.
420Sstevel@tonic-gate/
430Sstevel@tonic-gate
440Sstevel@tonic-gate#include "SYS.h"
450Sstevel@tonic-gate
460Sstevel@tonic-gate	ENTRY(__mul64)
470Sstevel@tonic-gate	push	%ebp
480Sstevel@tonic-gate	mov    	%esp,%ebp
490Sstevel@tonic-gate	pushl	%esi
500Sstevel@tonic-gate	mov	12(%ebp),%eax	/ A.hi (a)
510Sstevel@tonic-gate	mull	16(%ebp)	/ Multiply A.hi by B.lo (produces ad)
520Sstevel@tonic-gate	xchg	%ecx,%eax	/ ecx = bottom half of ad.
530Sstevel@tonic-gate	movl    8(%ebp),%eax	/ A.Lo (b)
540Sstevel@tonic-gate	movl	%eax,%esi	/ Save A.lo for later
550Sstevel@tonic-gate	mull	16(%ebp)	/ Multiply A.Lo by B.LO (dx:ax = bd.)
560Sstevel@tonic-gate	addl	%edx,%ecx	/ cx is ad
570Sstevel@tonic-gate	xchg	%eax,%esi       / esi is bd, eax = A.lo (d)
580Sstevel@tonic-gate	mull	20(%ebp)	/ Multiply A.lo * B.hi (producing bc)
590Sstevel@tonic-gate	addl	%ecx,%eax	/ Produce ad+bc
600Sstevel@tonic-gate	movl	%esi,%edx
610Sstevel@tonic-gate	xchg	%eax,%edx
620Sstevel@tonic-gate	popl	%esi
630Sstevel@tonic-gate	movl	%ebp,%esp
640Sstevel@tonic-gate	popl	%ebp
650Sstevel@tonic-gate	ret     $16
660Sstevel@tonic-gate	SET_SIZE(__mul64)
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