-/* This is an assembly language implementation of libgcc1.c for the sparc
- processor.
+/* This is an assembly language implementation of mulsi3, divsi3, and modsi3
+ for the sparc processor.
- These routines are derived from the Sparc Architecture Manual, version 8,
+ These routines are derived from the SPARC Architecture Manual, version 8,
slightly edited to match the desired calling convention, and also to
optimize them for our purposes. */
#endif
#ifdef L_divsi3
-.text
- .align 4
- .global .udiv
- .proc 4
+/*
+ * 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:
+ * .div name of function to generate
+ * div div=div => %o0 / %o1; div=rem => %o0 % %o1
+ * true true=true => signed; true=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.
+ */
+ .global .udiv
+ .align 4
+ .proc 4
+ .text
.udiv:
- save %sp, -64, %sp
- b divide
- mov 0, %l2 ! result always positive
- .global .div
- .proc 4
+ b ready_to_divide
+ mov 0, %g3 ! result is always positive
+
+ .global .div
+ .align 4
+ .proc 4
+ .text
.div:
- save %sp, -64, %sp
- orcc %i1, %i0, %g0 ! is either operand negative
- bge divide ! if not, skip this junk
- xor %i1, %i0, %l2 ! record sign of result in sign of %l2
- tst %i1
- bge 2f
- tst %i0
- ! %i1 < 0
- bge divide
- neg %i1
-2: ! %i0 < 0
- neg %i0
- ! FALL THROUGH
-divide:
- ! Compute size of quotient, scale comparand.
- orcc %i1, %g0, %l1 ! movcc %i1, %l1
- te 2 ! if %i1 = 0
- mov %i0, %i3
- mov 0, %i2
- sethi %hi(1<<(32-4-1)), %l3
- cmp %i3, %l3
+ ! compute sign of result; if neither is negative, no problem
+ orcc %o1, %o0, %g0 ! either negative?
+ bge ready_to_divide ! no, go do the divide
+ xor %o1, %o0, %g3 ! compute sign in any case
+ tst %o1
+ bge 1f
+ tst %o0
+ ! %o1 is definitely negative; %o0 might also be negative
+ bge ready_to_divide ! if %o0 not negative...
+ sub %g0, %o1, %o1 ! in any case, make %o1 nonneg
+1: ! %o0 is negative, %o1 is nonnegative
+ sub %g0, %o0, %o0 ! make %o0 nonnegative
+
+
+ready_to_divide:
+
+ ! 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 0x2 ! ST_DIV0
+ retl
+ clr %o0
+
+1:
+ cmp %o3, %o5 ! if %o1 exceeds %o0, done
+ blu got_result ! (and algorithm fails otherwise)
+ clr %o2
+ sethi %hi(1 << (32 - 4 - 1)), %g1
+ cmp %o3, %g1
blu not_really_big
- mov 0, %l0
- !
- ! Here, the %i0 is >= 2^(31-3) or so. We must be careful here,
- ! as our usual 3-at-a-shot divide step will cause overflow and havoc.
- ! The total number of bits in the result here is 3*%l0+%l4, where
- ! %l4 <= 3.
- ! Compute %l0 in an unorthodox manner: know we need to Shift %l1 into
- ! the top decade: so do not even bother to compare to %i3.
-1: cmp %l1, %l3
- bgeu 3f
- mov 1, %l4
- sll %l1, 3, %l1
- b 1b
- inc %l0
- !
- ! Now compute %l4
- !
-2: addcc %l1, %l1, %l1
- bcc not_too_big
- add %l4, 1, %l4
- !
- ! We are here if the %i1 overflowed when Shifting.
- ! This means that %i3 has the high-order bit set.
- ! Restore %l1 and subtract from %i3.
- sll %l3, 4, %l3
- srl %l1, 1, %l1
- add %l1, %l3, %l1
- b do_single_div
- dec %l4
-not_too_big:
-3: cmp %l1, %i3
- blu 2b
- nop
- be do_single_div
- nop
- ! %l1 > %i3: went too far: back up 1 step
- ! srl %l1, 1, %l1
- ! dec %l4
+ 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 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 do_single_div
+ sub %g2, 1, %g2
+
+ not_too_big:
+ 3: cmp %o5, %o3
+ blu 2b
+ nop
+ be 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 %i3 >= %l1, so we can do the
+ ! 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 %i3 >= 0. Because both %i3 and %l1 may have the
- ! high-order bit set in the first step, just falling into the regular
+ ! 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...
-do_single_div:
- deccc %l4
- bl end_regular_divide
- nop
- sub %i3, %l1, %i3
- mov 1, %i2
- b end_single_divloop
- nop
-single_divloop:
- sll %i2, 1, %i2
- bl 1f
- srl %l1, 1, %l1
- ! %i3 >= 0
- sub %i3, %l1, %i3
- b 2f
- inc %i2
-1: ! %i3 < 0
- add %i3, %l1, %i3
- dec %i2
-end_single_divloop:
-2: deccc %l4
- bge single_divloop
- tst %i3
- b end_regular_divide
- nop
+ do_single_div:
+ subcc %g2, 1, %g2
+ bl end_regular_divide
+ nop
+ sub %o3, %o5, %o3
+ mov 1, %o2
+ b end_single_divloop
+ nop
+ 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:
+ end_single_divloop:
+ subcc %g2, 1, %g2
+ bge single_divloop
+ tst %o3
+ b,a end_regular_divide
+
not_really_big:
-1: sll %l1, 3, %l1
- cmp %l1, %i3
+1:
+ sll %o5, 4, %o5
+ cmp %o5, %o3
bleu 1b
- inccc %l0
+ addcc %o4, 1, %o4
be got_result
- dec %l0
-do_regular_divide:
- ! Do the main division iteration
- tst %i3
- ! Fall through into divide loop
+ sub %o4, 1, %o4
+
+ tst %o3 ! set up for initial iteration
divloop:
- sll %i2, 3, %i2
+ sll %o2, 4, %o2
! depth 1, accumulated bits 0
- bl L.1.8
- srl %l1,1,%l1
+ bl L1.16
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
! depth 2, accumulated bits 1
- bl L.2.9
- srl %l1,1,%l1
+ bl L2.17
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
! depth 3, accumulated bits 3
- bl L.3.11
- srl %l1,1,%l1
+ bl L3.19
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ ! depth 4, accumulated bits 7
+ bl L4.23
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ b 9f
+ add %o2, (7*2+1), %o2
+
+L4.23:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ b 9f
+ add %o2, (7*2-1), %o2
+
+
+L3.19:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ ! depth 4, accumulated bits 5
+ bl L4.21
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
b 9f
- add %i2, (3*2+1), %i2
-L.3.11: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (5*2+1), %o2
+
+L4.21:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
b 9f
- add %i2, (3*2-1), %i2
-L.2.9: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (5*2-1), %o2
+
+L2.17:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
! depth 3, accumulated bits 1
- bl L.3.9
- srl %l1,1,%l1
+ bl L3.17
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
+ ! depth 4, accumulated bits 3
+ bl L4.19
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
b 9f
- add %i2, (1*2+1), %i2
-L.3.9: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (3*2+1), %o2
+
+L4.19:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
b 9f
- add %i2, (1*2-1), %i2
-L.1.8: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (3*2-1), %o2
+
+L3.17:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ ! depth 4, accumulated bits 1
+ bl L4.17
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ b 9f
+ add %o2, (1*2+1), %o2
+
+L4.17:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ b 9f
+ add %o2, (1*2-1), %o2
+
+L1.16:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
! depth 2, accumulated bits -1
- bl L.2.7
- srl %l1,1,%l1
+ bl L2.15
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
! depth 3, accumulated bits -1
- bl L.3.7
- srl %l1,1,%l1
+ bl L3.15
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ ! depth 4, accumulated bits -1
+ bl L4.15
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ b 9f
+ add %o2, (-1*2+1), %o2
+
+L4.15:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ b 9f
+ add %o2, (-1*2-1), %o2
+
+L3.15:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ ! depth 4, accumulated bits -3
+ bl L4.13
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
b 9f
- add %i2, (-1*2+1), %i2
-L.3.7: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (-3*2+1), %o2
+
+L4.13:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
b 9f
- add %i2, (-1*2-1), %i2
-L.2.7: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (-3*2-1), %o2
+
+L2.15:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
! depth 3, accumulated bits -3
- bl L.3.5
- srl %l1,1,%l1
+ bl L3.13
+ srl %o5,1,%o5
! remainder is positive
- subcc %i3,%l1,%i3
+ subcc %o3,%o5,%o3
+ ! depth 4, accumulated bits -5
+ bl L4.11
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
b 9f
- add %i2, (-3*2+1), %i2
-L.3.5: ! remainder is negative
- addcc %i3,%l1,%i3
+ add %o2, (-5*2+1), %o2
+
+L4.11:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
b 9f
- add %i2, (-3*2-1), %i2
+ add %o2, (-5*2-1), %o2
+
+L3.13:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ ! depth 4, accumulated bits -7
+ bl L4.9
+ srl %o5,1,%o5
+ ! remainder is positive
+ subcc %o3,%o5,%o3
+ b 9f
+ add %o2, (-7*2+1), %o2
+
+L4.9:
+ ! remainder is negative
+ addcc %o3,%o5,%o3
+ b 9f
+ add %o2, (-7*2-1), %o2
+
+ 9:
end_regular_divide:
-9: deccc %l0
+ subcc %o4, 1, %o4
bge divloop
- tst %i3
- bge got_result
- nop
- ! non-restoring fixup here
- dec %i2
+ tst %o3
+ bl,a got_result
+ ! non-restoring fixup here (one instruction only!)
+ sub %o2, 1, %o2
+
+
got_result:
- tst %l2
- bge 1f
- restore
- ! answer < 0
- retl ! leaf-routine return
- neg %o2, %o0 ! quotient <- -%i2
-1: retl ! leaf-routine return
- mov %o2, %o0 ! quotient <- %i2
+ ! check to see if answer should be < 0
+ tst %g3
+ bl,a 1f
+ sub %g0, %o2, %o2
+1:
+ retl
+ mov %o2, %o0
#endif
#ifdef L_modsi3
nop
be do_single_div
nop
- /* NB: these are commented out in the V8-Sparc manual as well */
+ /* 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
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