glibc/sysdeps/sparc/sparc32/udiv.S

   /* This file is generated from divrem.m4; DO NOT EDIT! */
/*
 * Division and remainder, from Appendix E of the Sparc Version 8
 * Architecture Manual, with fixes from Gordon Irlam.
 */

/*
 * Input: dividend and divisor in %o0 and %o1 respectively.
 *
 * m4 parameters:
 *  .udiv	name of function to generate
 *  div		div=div => %o0 / %o1; div=rem => %o0 % %o1
 *  false		false=true => signed; false=false => unsigned
 *
 * Algorithm parameters:
 *  N		how many bits per iteration we try to get (4)
 *  WORDSIZE	total number of bits (32)
 *
 * Derived constants:
 *  TOPBITS	number of bits in the top decade of a number
 *
 * Important variables:
 *  Q		the partial quotient under development (initially 0)
 *  R		the remainder so far, initially the dividend
 *  ITER	number of main division loop iterations required;
 *		equal to ceil(log2(quotient) / N).  Note that this
 *		is the log base (2^N) of the quotient.
 *  V		the current comparand, initially divisor*2^(ITER*N-1)
 *
 * Cost:
 *  Current estimate for non-large dividend is
 *	ceil(log2(quotient) / N) * (10 + 7N/2) + C
 *  A large dividend is one greater than 2^(31-TOPBITS) and takes a
 *  different path, as the upper bits of the quotient must be developed
 *  one bit at a time.
 */



#include <sysdep.h>
#include <sys/trap.h>

ENTRY(.udiv)

	! Ready to divide.  Compute size of quotient; scale comparand.
	orcc	%o1, %g0, %o5
	bne	1f
	mov	%o0, %o3

		! Divide by zero trap.  If it returns, return 0 (about as
		! wrong as possible, but that is what SunOS does...).
		ta	ST_DIV0
		retl
		clr	%o0

1:
	cmp	%o3, %o5			! if %o1 exceeds %o0, done
	blu	LOC(got_result)		! (and algorithm fails otherwise)
	clr	%o2
	sethi	%hi(1 << (32 - 4 - 1)), %g1
	cmp	%o3, %g1
	blu	LOC(not_really_big)
	clr	%o4

	! Here the dividend is >= 2**(31-N) or so.  We must be careful here,
	! as our usual N-at-a-shot divide step will cause overflow and havoc.
	! The 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 do not even bother to compare to R.
	1:
		cmp	%o5, %g1
		bgeu	3f
		mov	1, %g2
		sll	%o5, 4, %o5
		b	1b
		add	%o4, 1, %o4

	! Now compute %g2.
	2:	addcc	%o5, %o5, %o5
		bcc	LOC(not_too_big)
		add	%g2, 1, %g2

		! We get here if the %o1 overflowed while shifting.
		! This means that %o3 has the high-order bit set.
		! Restore %o5 and subtract from %o3.
		sll	%g1, 4, %g1	! high order bit
		srl	%o5, 1, %o5		! rest of %o5
		add	%o5, %g1, %o5
		b	LOC(do_single_div)
		sub	%g2, 1, %g2

	LOC(not_too_big):
	3:	cmp	%o5, %o3
		blu	2b
		nop
		be	LOC(do_single_div)
		nop
	/* NB: these are commented out in the V8-Sparc manual as well */
	/* (I do not understand this) */
	! %o5 > %o3: went too far: back up 1 step
	!	srl	%o5, 1, %o5
	!	dec	%g2
	! do single-bit divide steps
	!
	! We have to be careful here.  We know that %o3 >= %o5, so we can do the
	! first divide step without thinking.  BUT, the others are conditional,
	! and are only done if %o3 >= 0.  Because both %o3 and %o5 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...
	LOC(do_single_div):
		subcc	%g2, 1, %g2
		bl	LOC(end_regular_divide)
		nop
		sub	%o3, %o5, %o3
		mov	1, %o2
		b	LOC(end_single_divloop)
		nop
	LOC(single_divloop):
		sll	%o2, 1, %o2
		bl	1f
		srl	%o5, 1, %o5
		! %o3 >= 0
		sub	%o3, %o5, %o3
		b	2f
		add	%o2, 1, %o2
	1:	! %o3 < 0
		add	%o3, %o5, %o3
		sub	%o2, 1, %o2
	2:
	LOC(end_single_divloop):
		subcc	%g2, 1, %g2
		bge	LOC(single_divloop)
		tst	%o3
		b,a	LOC(end_regular_divide)

LOC(not_really_big):
1:
	sll	%o5, 4, %o5
	cmp	%o5, %o3
	bleu	1b
	addcc	%o4, 1, %o4
	be	LOC(got_result)
	sub	%o4, 1, %o4

	tst	%o3	! set up for initial iteration
LOC(divloop):
	sll	%o2, 4, %o2
		! depth 1, accumulated bits 0
	bl	LOC(1.16)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 2, accumulated bits 1
	bl	LOC(2.17)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 3, accumulated bits 3
	bl	LOC(3.19)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 4, accumulated bits 7
	bl	LOC(4.23)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (7*2+1), %o2

LOC(4.23):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (7*2-1), %o2


LOC(3.19):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 4, accumulated bits 5
	bl	LOC(4.21)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (5*2+1), %o2

LOC(4.21):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (5*2-1), %o2



LOC(2.17):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 3, accumulated bits 1
	bl	LOC(3.17)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 4, accumulated bits 3
	bl	LOC(4.19)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (3*2+1), %o2

LOC(4.19):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (3*2-1), %o2


LOC(3.17):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 4, accumulated bits 1
	bl	LOC(4.17)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (1*2+1), %o2

LOC(4.17):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (1*2-1), %o2




LOC(1.16):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 2, accumulated bits -1
	bl	LOC(2.15)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 3, accumulated bits -1
	bl	LOC(3.15)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 4, accumulated bits -1
	bl	LOC(4.15)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-1*2+1), %o2

LOC(4.15):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-1*2-1), %o2


LOC(3.15):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 4, accumulated bits -3
	bl	LOC(4.13)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-3*2+1), %o2

LOC(4.13):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-3*2-1), %o2



LOC(2.15):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 3, accumulated bits -3
	bl	LOC(3.13)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
			! depth 4, accumulated bits -5
	bl	LOC(4.11)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-5*2+1), %o2

LOC(4.11):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-5*2-1), %o2


LOC(3.13):
	! remainder is negative
	addcc	%o3,%o5,%o3
			! depth 4, accumulated bits -7
	bl	LOC(4.9)
	srl	%o5,1,%o5
	! remainder is positive
	subcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-7*2+1), %o2

LOC(4.9):
	! remainder is negative
	addcc	%o3,%o5,%o3
		b	9f
		add	%o2, (-7*2-1), %o2




	9:
LOC(end_regular_divide):
	subcc	%o4, 1, %o4
	bge	LOC(divloop)
	tst	%o3
	bl,a	LOC(got_result)
	! non-restoring fixup here (one instruction only!)
	sub	%o2, 1, %o2


LOC(got_result):

	retl
	mov %o2, %o0

END(.udiv)