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#
#   File rnd.S            Created 04-FEB-1999        Richard B. Johnson
#
#   Simple random number generator. Based upon Alan R. Miller's
#   algorithm. Professor of Metallurgy, University of New Mexico
#   Institute of Mining and Technology, circa 1980. Published
#   In the 8080/Z-80 Assembly Language manual he wrote.
#
#   unsigned size_t rnd((size_t *) seed);
#
#   The seed can be initialized with time(&seed); on each boot.
#

MAGIC  = 0x72b6078b 
INTPTR = 0x08
DIVISR = 0x0c
.section	.text
.global		rnd
.type		rnd,@function
.align	0x04
rnd:	pushl	%ebx
	movl	INTPTR(%esp), %ebx
	movl	(%ebx), %eax
	rorl	$3, %eax
	addl	$MAGIC, %eax
	movl	%eax, (%ebx)
	popl	%ebx
        ret

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#
#	This returns a random number between 0 and one less than the
#	input divisor, i.e. n mod rand(x).
#
#	size_t modrnd((size_t *) seed, size_t divisor);
#
.type	modrnd,@function
.global	modrnd
.align	0x04

modrnd:	pushl	%ebx
	movl	INTPTR(%esp), %ebx
	movl	(%ebx), %eax
	rorl	$3, %eax
	addl	$MAGIC, %eax
	movl	%eax, (%ebx)
	xorl	%edx, %edx
	divl	DIVISR(%esp)
	movl	%edx, %eax
	popl	%ebx
        ret
.end
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