/* 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:
* .urem name of function to generate
* rem rem=div => %o0 / %o1; rem=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(.urem)
! 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!)
add %o3, %o1, %o3
LOC(got_result):
retl
mov %o3, %o0
END(.urem)