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Diffstat (limited to 'sysdeps/alpha/divq.S')
| -rw-r--r-- | sysdeps/alpha/divq.S | 273 |
1 files changed, 273 insertions, 0 deletions
diff --git a/sysdeps/alpha/divq.S b/sysdeps/alpha/divq.S new file mode 100644 index 0000000000..c552bd2477 --- /dev/null +++ b/sysdeps/alpha/divq.S @@ -0,0 +1,273 @@ +/* Copyright (C) 2004-2014 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library. If not, see + <http://www.gnu.org/licenses/>. */ + +#include "div_libc.h" + + +/* 64-bit signed long divide. These are not normal C functions. Argument + registers are t10 and t11, the result goes in t12. Only t12 and AT may + be clobbered. + + Theory of operation here is that we can use the FPU divider for virtually + all operands that we see: all dividend values between -2**53 and 2**53-1 + can be computed directly. Note that divisor values need not be checked + against that range because the rounded fp value will be close enough such + that the quotient is < 1, which will properly be truncated to zero when we + convert back to integer. + + When the dividend is outside the range for which we can compute exact + results, we use the fp quotent as an estimate from which we begin refining + an exact integral value. This reduces the number of iterations in the + shift-and-subtract loop significantly. + + The FPCR save/restore is due to the fact that the EV6 _will_ set FPCR_INE + for cvttq/c even without /sui being set. It will not, however, properly + raise the exception, so we don't have to worry about FPCR_INED being clear + and so dying by SIGFPE. */ + + .text + .align 4 + .globl __divq + .type __divq, @funcnoplt + .usepv __divq, no + + cfi_startproc + cfi_return_column (RA) +__divq: + lda sp, -FRAME(sp) + cfi_def_cfa_offset (FRAME) + CALL_MCOUNT + + /* Get the fp divide insn issued as quickly as possible. After + that's done, we have at least 22 cycles until its results are + ready -- all the time in the world to figure out how we're + going to use the results. */ + stt $f0, 0(sp) + excb + beq Y, DIVBYZERO + + stt $f1, 8(sp) + stt $f3, 48(sp) + cfi_rel_offset ($f0, 0) + cfi_rel_offset ($f1, 8) + cfi_rel_offset ($f3, 48) + mf_fpcr $f3 + + _ITOFT2 X, $f0, 16, Y, $f1, 24 + cvtqt $f0, $f0 + cvtqt $f1, $f1 + divt/c $f0, $f1, $f0 + + /* Check to see if X fit in the double as an exact value. */ + sll X, (64-53), AT + ldt $f1, 8(sp) + sra AT, (64-53), AT + cmpeq X, AT, AT + beq AT, $x_big + + /* If we get here, we're expecting exact results from the division. + Do nothing else besides convert and clean up. */ + cvttq/c $f0, $f0 + excb + mt_fpcr $f3 + _FTOIT $f0, RV, 16 + + ldt $f0, 0(sp) + ldt $f3, 48(sp) + cfi_restore ($f1) + cfi_remember_state + cfi_restore ($f0) + cfi_restore ($f3) + cfi_def_cfa_offset (0) + lda sp, FRAME(sp) + ret $31, (RA), 1 + + .align 4 + cfi_restore_state +$x_big: + /* If we get here, X is large enough that we don't expect exact + results, and neither X nor Y got mis-translated for the fp + division. Our task is to take the fp result, figure out how + far it's off from the correct result and compute a fixup. */ + stq t0, 16(sp) + stq t1, 24(sp) + stq t2, 32(sp) + stq t5, 40(sp) + cfi_rel_offset (t0, 16) + cfi_rel_offset (t1, 24) + cfi_rel_offset (t2, 32) + cfi_rel_offset (t5, 40) + +#define Q RV /* quotient */ +#define R t0 /* remainder */ +#define SY t1 /* scaled Y */ +#define S t2 /* scalar */ +#define QY t3 /* Q*Y */ + + /* The fixup code below can only handle unsigned values. */ + or X, Y, AT + mov $31, t5 + blt AT, $fix_sign_in +$fix_sign_in_ret1: + cvttq/c $f0, $f0 + + _FTOIT $f0, Q, 8 + .align 3 +$fix_sign_in_ret2: + ldt $f0, 0(sp) + stq t3, 0(sp) + cfi_restore ($f0) + cfi_rel_offset (t3, 0) + + mulq Q, Y, QY + excb + stq t4, 8(sp) + mt_fpcr $f3 + cfi_rel_offset (t4, 8) + + subq QY, X, R + mov Y, SY + mov 1, S + bgt R, $q_high + +$q_high_ret: + subq X, QY, R + mov Y, SY + mov 1, S + bgt R, $q_low + +$q_low_ret: + ldq t0, 16(sp) + ldq t1, 24(sp) + ldq t2, 32(sp) + bne t5, $fix_sign_out + +$fix_sign_out_ret: + ldq t3, 0(sp) + ldq t4, 8(sp) + ldq t5, 40(sp) + ldt $f3, 48(sp) + lda sp, FRAME(sp) + cfi_remember_state + cfi_restore (t0) + cfi_restore (t1) + cfi_restore (t2) + cfi_restore (t3) + cfi_restore (t4) + cfi_restore (t5) + cfi_restore ($f3) + cfi_def_cfa_offset (0) + ret $31, (RA), 1 + + .align 4 + cfi_restore_state + /* The quotient that we computed was too large. We need to reduce + it by S such that Y*S >= R. Obviously the closer we get to the + correct value the better, but overshooting high is ok, as we'll + fix that up later. */ +0: + addq SY, SY, SY + addq S, S, S +$q_high: + cmpult SY, R, AT + bne AT, 0b + + subq Q, S, Q + unop + subq QY, SY, QY + br $q_high_ret + + .align 4 + /* The quotient that we computed was too small. Divide Y by the + current remainder (R) and add that to the existing quotient (Q). + The expectation, of course, is that R is much smaller than X. */ + /* Begin with a shift-up loop. Compute S such that Y*S >= R. We + already have a copy of Y in SY and the value 1 in S. */ +0: + addq SY, SY, SY + addq S, S, S +$q_low: + cmpult SY, R, AT + bne AT, 0b + + /* Shift-down and subtract loop. Each iteration compares our scaled + Y (SY) with the remainder (R); if SY <= R then X is divisible by + Y's scalar (S) so add it to the quotient (Q). */ +2: addq Q, S, t3 + srl S, 1, S + cmpule SY, R, AT + subq R, SY, t4 + + cmovne AT, t3, Q + cmovne AT, t4, R + srl SY, 1, SY + bne S, 2b + + br $q_low_ret + + .align 4 +$fix_sign_in: + /* If we got here, then X|Y is negative. Need to adjust everything + such that we're doing unsigned division in the fixup loop. */ + /* T5 records the changes we had to make: + bit 0: set if result should be negative. + bit 2: set if X was negated. + bit 3: set if Y was negated. + */ + xor X, Y, AT + cmplt AT, 0, t5 + cmplt X, 0, AT + negq X, t0 + + s4addq AT, t5, t5 + cmovne AT, t0, X + cmplt Y, 0, AT + negq Y, t0 + + s8addq AT, t5, t5 + cmovne AT, t0, Y + unop + blbc t5, $fix_sign_in_ret1 + + cvttq/c $f0, $f0 + _FTOIT $f0, Q, 8 + .align 3 + negq Q, Q + br $fix_sign_in_ret2 + + .align 4 +$fix_sign_out: + /* Now we get to undo what we did above. */ + /* ??? Is this really faster than just increasing the size of + the stack frame and storing X and Y in memory? */ + and t5, 8, AT + negq Y, t4 + cmovne AT, t4, Y + + and t5, 4, AT + negq X, t4 + cmovne AT, t4, X + + negq RV, t4 + cmovlbs t5, t4, RV + + br $fix_sign_out_ret + + cfi_endproc + .size __divq, .-__divq + + DO_DIVBYZERO |