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347 lines
6.8 KiB
ArmAsm
347 lines
6.8 KiB
ArmAsm
/* This file is generated from divrem.m4; DO NOT EDIT! */
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/*
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* Division and remainder, from Appendix E of the Sparc Version 8
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* Architecture Manual, with fixes from Gordon Irlam.
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*/
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/*
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* Input: dividend and divisor in %o0 and %o1 respectively.
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*
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* m4 parameters:
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* .urem name of function to generate
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* rem rem=div => %o0 / %o1; rem=rem => %o0 % %o1
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* false false=true => signed; false=false => unsigned
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*
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* Algorithm parameters:
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* N how many bits per iteration we try to get (4)
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* WORDSIZE total number of bits (32)
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*
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* Derived constants:
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* TOPBITS number of bits in the top decade of a number
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*
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* Important variables:
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* Q the partial quotient under development (initially 0)
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* R the remainder so far, initially the dividend
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* ITER number of main division loop iterations required;
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* equal to ceil(log2(quotient) / N). Note that this
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* is the log base (2^N) of the quotient.
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* V the current comparand, initially divisor*2^(ITER*N-1)
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*
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* Cost:
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* Current estimate for non-large dividend is
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* ceil(log2(quotient) / N) * (10 + 7N/2) + C
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* A large dividend is one greater than 2^(31-TOPBITS) and takes a
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* different path, as the upper bits of the quotient must be developed
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* one bit at a time.
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*/
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#include <sysdep.h>
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#include <sys/trap.h>
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ENTRY(.urem)
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! Ready to divide. Compute size of quotient; scale comparand.
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orcc %o1, %g0, %o5
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bne 1f
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mov %o0, %o3
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! Divide by zero trap. If it returns, return 0 (about as
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! wrong as possible, but that is what SunOS does...).
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ta ST_DIV0
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retl
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clr %o0
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1:
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cmp %o3, %o5 ! if %o1 exceeds %o0, done
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blu LOC(got_result) ! (and algorithm fails otherwise)
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clr %o2
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sethi %hi(1 << (32 - 4 - 1)), %g1
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cmp %o3, %g1
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blu LOC(not_really_big)
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clr %o4
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! Here the dividend is >= 2**(31-N) or so. We must be careful here,
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! as our usual N-at-a-shot divide step will cause overflow and havoc.
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! The number of bits in the result here is N*ITER+SC, where SC <= N.
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! Compute ITER in an unorthodox manner: know we need to shift V into
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! the top decade: so do not even bother to compare to R.
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1:
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cmp %o5, %g1
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bgeu 3f
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mov 1, %g2
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sll %o5, 4, %o5
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b 1b
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add %o4, 1, %o4
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! Now compute %g2.
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2: addcc %o5, %o5, %o5
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bcc LOC(not_too_big)
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add %g2, 1, %g2
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! We get here if the %o1 overflowed while shifting.
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! This means that %o3 has the high-order bit set.
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! Restore %o5 and subtract from %o3.
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sll %g1, 4, %g1 ! high order bit
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srl %o5, 1, %o5 ! rest of %o5
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add %o5, %g1, %o5
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b LOC(do_single_div)
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sub %g2, 1, %g2
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LOC(not_too_big):
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3: cmp %o5, %o3
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blu 2b
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nop
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be LOC(do_single_div)
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nop
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/* NB: these are commented out in the V8-Sparc manual as well */
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/* (I do not understand this) */
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! %o5 > %o3: went too far: back up 1 step
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! srl %o5, 1, %o5
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! dec %g2
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! do single-bit divide steps
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!
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! We have to be careful here. We know that %o3 >= %o5, so we can do the
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! first divide step without thinking. BUT, the others are conditional,
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! and are only done if %o3 >= 0. Because both %o3 and %o5 may have the high-
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! order bit set in the first step, just falling into the regular
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! division loop will mess up the first time around.
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! So we unroll slightly...
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LOC(do_single_div):
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subcc %g2, 1, %g2
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bl LOC(end_regular_divide)
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nop
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sub %o3, %o5, %o3
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mov 1, %o2
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b LOC(end_single_divloop)
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nop
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LOC(single_divloop):
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sll %o2, 1, %o2
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bl 1f
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srl %o5, 1, %o5
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! %o3 >= 0
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sub %o3, %o5, %o3
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b 2f
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add %o2, 1, %o2
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1: ! %o3 < 0
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add %o3, %o5, %o3
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sub %o2, 1, %o2
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2:
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LOC(end_single_divloop):
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subcc %g2, 1, %g2
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bge LOC(single_divloop)
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tst %o3
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b,a LOC(end_regular_divide)
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LOC(not_really_big):
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1:
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sll %o5, 4, %o5
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cmp %o5, %o3
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bleu 1b
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addcc %o4, 1, %o4
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be LOC(got_result)
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sub %o4, 1, %o4
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tst %o3 ! set up for initial iteration
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LOC(divloop):
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sll %o2, 4, %o2
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! depth 1, accumulated bits 0
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bl LOC(1.16)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 2, accumulated bits 1
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bl LOC(2.17)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 3, accumulated bits 3
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bl LOC(3.19)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 4, accumulated bits 7
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bl LOC(4.23)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (7*2+1), %o2
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LOC(4.23):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (7*2-1), %o2
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LOC(3.19):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 4, accumulated bits 5
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bl LOC(4.21)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (5*2+1), %o2
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LOC(4.21):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (5*2-1), %o2
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LOC(2.17):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 3, accumulated bits 1
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bl LOC(3.17)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 4, accumulated bits 3
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bl LOC(4.19)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (3*2+1), %o2
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LOC(4.19):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (3*2-1), %o2
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LOC(3.17):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 4, accumulated bits 1
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bl LOC(4.17)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (1*2+1), %o2
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LOC(4.17):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (1*2-1), %o2
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LOC(1.16):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 2, accumulated bits -1
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bl LOC(2.15)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 3, accumulated bits -1
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bl LOC(3.15)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 4, accumulated bits -1
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bl LOC(4.15)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (-1*2+1), %o2
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LOC(4.15):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (-1*2-1), %o2
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LOC(3.15):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 4, accumulated bits -3
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bl LOC(4.13)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (-3*2+1), %o2
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LOC(4.13):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (-3*2-1), %o2
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LOC(2.15):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 3, accumulated bits -3
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bl LOC(3.13)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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! depth 4, accumulated bits -5
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bl LOC(4.11)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (-5*2+1), %o2
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LOC(4.11):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (-5*2-1), %o2
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LOC(3.13):
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! remainder is negative
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addcc %o3,%o5,%o3
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! depth 4, accumulated bits -7
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bl LOC(4.9)
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srl %o5,1,%o5
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! remainder is positive
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subcc %o3,%o5,%o3
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b 9f
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add %o2, (-7*2+1), %o2
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LOC(4.9):
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! remainder is negative
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addcc %o3,%o5,%o3
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b 9f
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add %o2, (-7*2-1), %o2
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9:
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LOC(end_regular_divide):
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subcc %o4, 1, %o4
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bge LOC(divloop)
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tst %o3
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bl,a LOC(got_result)
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! non-restoring fixup here (one instruction only!)
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add %o3, %o1, %o3
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LOC(got_result):
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retl
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mov %o3, %o0
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END(.urem)
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