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Power 6/32 Unix version 1.2b

/* 	modf.x	4.2	84/02/27	*/

/* 
*  double modf (value, iptr)
*  double value, *iptr;
* 
*  Modf returns the fractional part of "value",
*  and stores the integer part indirectly through "iptr".
*/ 
#include	<machine/fp.h>
 
	.text
	.globl	_modf
_modf:	.word	0x1ffc		/* we use r2,r3,r4,r5 */

 /*
 * Some initializations:
 */
	ldd	4(fp)		/* load accumulator, for converison	*/
	cvdl	r2		/*  to an integer.			*/
	bvs	gsb		/* iff too big grunt it out		*/
	cvld	r2		/* float the integer part		*/
	std	r2
	ldd	4(fp)		/* isolate the fraction			*/
	subd	r2
	std	r0
	movl	12(fp),r6	/* get int return address */
	movl	r2,(r6)
	movl	r3,4(r6)
	ret
gsb:	clrl	r3
	movl	4(fp),r0	/* fetch operand to r0,r1. */
	movl	8(fp),r1	
	movl	12(fp),r6	/* fetch addr of int to r6. */
 /*
 * get exponent
 */
	andl3	$EXPMASK,r0,r2	/* r2 will hold the exponent. */
	jeql	is_reserved	/* check for reserved operand.  */
	shrl	$EXPSHIFT,r2,r2
	subl2	$BIAS,r2	/* unbias it.  */
	jleq	allfrac		/* it's int part is  zero. */
	cmpl	r2,$56
	jgeq	allint		/* it's fraction part is zero. */
 /*
 * get fraction
 */
	movl	r0,r4		/* remember the original number. */
	movl	r1,r5
	bbc	$31,r0,positive	/* if negative remember it. */
	incl	r3
positive:
				/* clear the non fraction parts. */
	andl2	$(0!(EXPMASK | SIGNBIT)),r0
				/* add the hidden bit. */
	orl2	$(0!CLEARHID),r0

	cmpl	r2,$HID_POS	/* see if there are bits to clear only in r0 */
				/* or r1 has to be taken care of. */
				/* ( for fraction calculation) */

	jgtr	in_r1		/* some bytes in r1. */

	jeql	onlyallr0	/* all r0 must be cleared,r1 unchanged. */

				/* only r0 must be canged. */
	mnegl	r2,r7		/* r7 - loop counter. */
	movl	$CLEARHID,r8	/* first bit to clear. */
1:
	andl2	r8,r0		/* clear int. bits from fraction part. */
	shar	$1,r8,r8
	aoblss	$0,r7,1b
1:
	andl2	r8,r4		/* clear frac bits for int calculation: */
	shar	$1,r8,r8
	cmpl	$0xffffffff,r8
	jneq	1b
	clrl	r5
	jmp	norm

onlyallr0:
	clrl	r0
	clrl	r5
	jmp 	norm

in_r1:
	clrl	r0		/* clear int part for frac. calculation. */
	subl3	r2,$HID_POS,r7
	movl	$0x7fffffff,r8
1:
	andl2	r8,r1
	shar	$1,r8,r8
	orl2	$0x80000000,r8		/* force the 'sign' bit to be on. */
	aoblss	$0,r7,1b
1:
	andl2	r8,r5
	shar	$1,r8,r8
	cmpl	$0xffffffff,r8
	jneq	1b

norm:
	addl2	$BIAS,r2	/* fnorm expects it biased. */
	callf	$4,fnorm	/* normelize fraction part. */
	cmpl	$0,r0
	jeql	1f
	bbc	$0,r3,1f
	orl2	$0x80000000,r0
1:
	movl	r4,(r6)		/* put int part in place. */
	movl	r5,4(r6)
	ret
 
allint:
	movl	r0,(r6)		/* copy the argument to the int addr. */
	movl	r1,4(r6)
	clrl	r0		/* clear the fraction part. */
	clrl	r1
	ret

allfrac:
				/* the fraction is ready in r0,r1. */
	clrl	(r6)		/* zero the int part. */
	clrl	4(r6)
	ret





ret_zero:
	clrl	(r6)
	clrl	4(r6)
	clrl	r0
	clrl	r1
	ret

is_reserved:
	bbc	$31,r0,ret_zero
	callf 	$4,fpresop
	ret
	

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