xref: /freebsd/contrib/llvm-project/compiler-rt/lib/builtins/sparc64/divmod.m4 (revision 0b57cec536236d46e3dba9bd041533462f33dbb7)

/*
 * This m4 code has been taken from The SPARC Architecture Manual Version 8.
 */

/*
 * Division/Remainder
 *
 * Input is:
 *   dividend -- the thing being divided
 *   divisor -- how many ways to divide it
 * Important parameters:
 *   N -- how many bits per iteration we try to get
 *        as our current guess: define(N, 4) define(TWOSUPN, 16)
 *   WORDSIZE -- how many bits altogether we're talking about:
 *               obviously: define(WORDSIZE, 32)
 * A derived constant:
 *   TOPBITS -- how many bits are in the top "decade" of a number:
 *        define(TOPBITS, eval( WORDSIZE - N*((WORDSIZE-1)/N) ) )
 * Important variables are:
 *   Q -- the partial quotient under development -- initially 0
 *   R -- the remainder so far -- initially == the dividend
 *   ITER -- number of iterations of the main division loop which will
 *           be required. Equal to CEIL( lg2(quotient)/N )
 *           Note that this is log_base_(2ˆN) of the quotient.
 *   V -- the current comparand -- initially divisor*2ˆ(ITER*N-1)
 * Cost:
 *   current estimate for non-large dividend is
 *        CEIL( lg2(quotient) / N ) x ( 10 + 7N/2 ) + C
 *   a large dividend is one greater than 2ˆ(31-TOPBITS) and takes a
 *   different path, as the upper bits of the quotient must be developed
 *   one bit at a time.
 *   This uses the m4 and cpp macro preprocessors.
 */

define(dividend, `%o0')
define(divisor,`%o1')
define(Q, `%o2')
define(R, `%o3')
define(ITER, `%o4')
define(V, `%o5')
define(SIGN, `%g3')
define(T, `%g1')
define(SC,`%g2')
/*
 * This is the recursive definition of how we develop quotient digits.
 * It takes three important parameters:
 *   $1 -- the current depth, 1<=$1<=N
 *   $2 -- the current accumulation of quotient bits
 *   N -- max depth
 * We add a new bit to $2 and either recurse or insert the bits in the quotient.
 * Dynamic input:
 *   R -- current remainder
 *   Q -- current quotient
 *   V -- current comparand
 *   cc -- set on current value of R
 * Dynamic output:
 *   R', Q', V', cc'
 */

#include "../assembly.h"

define(DEVELOP_QUOTIENT_BITS,
`	!depth $1, accumulated bits $2
	bl	L.$1.eval(TWOSUPN+$2)
	srl	V,1,V
	! remainder is nonnegative
	subcc	R,V,R
	ifelse( $1, N,
	`	b	9f
		add	Q, ($2*2+1), Q
	',` DEVELOP_QUOTIENT_BITS( incr($1), `eval(2*$2+1)')
	')
L.$1.eval(TWOSUPN+$2):
	! remainder is negative
	addcc	R,V,R
	ifelse( $1, N,
	`	b	9f
		add	Q, ($2*2-1), Q
	',` DEVELOP_QUOTIENT_BITS( incr($1), `eval(2*$2-1)')
	')
	ifelse( $1, 1, `9:')
')
ifelse( ANSWER, `quotient', `
.text
	.align 32
DEFINE_COMPILERRT_FUNCTION(__udivsi3)
	b	divide
	mov	0,SIGN			! result always nonnegative
.text
	.align 32
DEFINE_COMPILERRT_FUNCTION(__divsi3)
	orcc	divisor,dividend,%g0	! are either dividend or divisor negative
	bge	divide			! if not, skip this junk
	xor	divisor,dividend,SIGN	! record sign of result in sign of SIGN
	tst	divisor
	bge	2f
	tst	dividend
	! divisor < 0
	bge	divide
	neg	divisor
	2:
	! dividend < 0
	neg	dividend
	! FALL THROUGH
',`
.text
	.align 32
DEFINE_COMPILERRT_FUNCTION(__umodsi3)
	b	divide
	mov	0,SIGN			! result always nonnegative
.text
	.align 32
DEFINE_COMPILERRT_FUNCTION(__modsi3)
	orcc	divisor,dividend,%g0	! are either dividend or divisor negative
	bge	divide			! if not, skip this junk
	mov	dividend,SIGN		! record sign of result in sign of SIGN
	tst	divisor
	bge	2f
	tst	dividend
	! divisor < 0
	bge	divide
	neg	divisor
	2:
	! dividend < 0
	neg	dividend
	! FALL THROUGH
')

divide:
	! Compute size of quotient, scale comparand.
	orcc	divisor,%g0,V		! movcc divisor,V
	te	2			! if divisor = 0
	mov	dividend,R
	mov	0,Q
	sethi	%hi(1<<(WORDSIZE-TOPBITS-1)),T
	cmp	R,T
	blu	not_really_big
	mov	0,ITER
	!
	! Here, the dividend is >= 2ˆ(31-N) or so. We must be careful here,
	! as our usual N-at-a-shot divide step will cause overflow and havoc.
	! The total number of bits in the result here is N*ITER+SC, where
	! SC <= N.
	! Compute ITER in an unorthodox manner: know we need to Shift V into
! the top decade: so don't even bother to compare to R.
1:
	cmp	V,T
	bgeu	3f
	mov	1,SC
	sll	V,N,V
	b	1b
	inc	ITER
! Now compute SC
2:	addcc	V,V,V
	bcc	not_too_big
	add	SC,1,SC
		! We're here if the divisor overflowed when Shifting.
		! This means that R has the high-order bit set.
		! Restore V and subtract from R.
		sll	T,TOPBITS,T	! high order bit
		srl	V,1,V		! rest of V
		add	V,T,V
		b	do_single_div
		dec	SC
not_too_big:
3:	cmp	V,R
	blu	2b
	nop
	be	do_single_div
	nop
! V > R: went too far: back up 1 step
!     srl V,1,V
!      dec SC
! do single-bit divide steps
!
! We have to be careful here. We know that R >= V, so we can do the
! first divide step without thinking. BUT, the others are conditional,
! and are only done if R >= 0. Because both R and V may have the high-
! order bit set in the first step, just falling into the regular
! division loop will mess up the first time around.
! So we unroll slightly...
do_single_div:
	deccc	SC
	bl	end_regular_divide
	nop
	sub	R,V,R
	mov	1,Q
	b,a	end_single_divloop
	! EMPTY
single_divloop:
	sll	Q,1,Q
	bl	1f
	srl	V,1,V
	! R >= 0
		sub	R,V,R
		b	2f
		inc	Q
	1:	! R < 0
		add	R,V,R
		dec	Q
	2:
	end_single_divloop:
		deccc	SC
		bge	single_divloop
		tst	R
		b,a	end_regular_divide
		! EMPTY

not_really_big:
1:
	sll	V,N,V
	cmp	V,R
	bleu	1b
	inccc	ITER
	be	got_result
	dec	ITER
do_regular_divide:
	! Do the main division iteration
	tst	R
	! Fall through into divide loop
divloop:
	sll	Q,N,Q
	DEVELOP_QUOTIENT_BITS( 1, 0 )
end_regular_divide:
	deccc	ITER
	bge	divloop
	tst	R
	bl,a	got_result
	! non-restoring fixup if remainder < 0, otherwise annulled
ifelse( ANSWER, `quotient',
`	dec	Q
',`	add	R,divisor,R
')

got_result:
	tst	SIGN
	bl,a	1f
	! negate for answer < 0, otherwise annulled
ifelse( ANSWER, `quotient',
`	neg	%o2,%o2			! Q <- -Q
',`	neg	%o3,%o3 		! R <- -R
')
1:
	retl				! leaf-routine return
ifelse( ANSWER, `quotient',
`	mov	%o2,%o0			! quotient <- Q
',`	mov	%o3,%o0			! remainder <- R
')