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Diffstat (limited to 'sysdeps/alpha/divqu.S')
| -rw-r--r-- | sysdeps/alpha/divqu.S | 244 |
1 files changed, 244 insertions, 0 deletions
diff --git a/sysdeps/alpha/divqu.S b/sysdeps/alpha/divqu.S new file mode 100644 index 0000000000..6ff6c035e2 --- /dev/null +++ b/sysdeps/alpha/divqu.S @@ -0,0 +1,244 @@ +/* Copyright (C) 2004 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, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +#include "div_libc.h" + + +/* 64-bit unsigned 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. */ + + .text + .align 4 + .globl __divqu + .type __divqu, @function + .usepv __divqu, no + + cfi_startproc + cfi_return_column (RA) +__divqu: + 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. */ + stq X, 16(sp) + stq Y, 24(sp) + beq Y, DIVBYZERO + + stt $f0, 0(sp) + stt $f1, 8(sp) + cfi_rel_offset ($f0, 0) + cfi_rel_offset ($f1, 8) + ldt $f0, 16(sp) + ldt $f1, 24(sp) + + cvtqt $f0, $f0 + cvtqt $f1, $f1 + blt X, $x_is_neg + divt/c $f0, $f1, $f0 + + /* Check to see if Y was mis-converted as signed value. */ + ldt $f1, 8(sp) + unop + nop + blt Y, $y_is_neg + + /* Check to see if X fit in the double as an exact value. */ + srl X, 53, AT + bne 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 + stt $f0, 16(sp) + + ldq RV, 16(sp) + ldt $f0, 0(sp) + cfi_remember_state + cfi_restore ($f0) + cfi_restore ($f1) + cfi_def_cfa_offset (0) + lda sp, FRAME(sp) + ret $31, (RA), 1 + + .align 4 + cfi_restore_state +$x_is_neg: + /* If we get here, X is so big that bit 63 is set, which made the + conversion come out negative. Fix it up lest we not even get + a good estimate. */ + ldah AT, 0x5f80 /* 2**64 as float. */ + stt $f2, 24(sp) + cfi_rel_offset ($f2, 24) + stl AT, 16(sp) + lds $f2, 16(sp) + + addt $f0, $f2, $f0 + unop + divt/c $f0, $f1, $f0 + unop + + /* Ok, we've now the divide issued. Continue with other checks. */ + ldt $f1, 8(sp) + unop + ldt $f2, 24(sp) + blt Y, $y_is_neg + cfi_restore ($f1) + cfi_restore ($f2) + cfi_remember_state /* for y_is_neg */ + + .align 4 +$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 t3, 40(sp) + cfi_rel_offset (t0, 16) + cfi_rel_offset (t1, 24) + cfi_rel_offset (t2, 32) + cfi_rel_offset (t3, 40) + +#define Q RV /* quotient */ +#define R t0 /* remainder */ +#define SY t1 /* scaled Y */ +#define S t2 /* scalar */ +#define QY t3 /* Q*Y */ + + cvttq/c $f0, $f0 + stt $f0, 8(sp) + ldq Q, 8(sp) + mulq Q, Y, QY + + stq t4, 8(sp) + unop + ldt $f0, 0(sp) + unop + cfi_rel_offset (t4, 8) + cfi_restore ($f0) + + 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 t4, 8(sp) + ldq t0, 16(sp) + ldq t1, 24(sp) + ldq t2, 32(sp) + + ldq t3, 40(sp) + lda sp, FRAME(sp) + cfi_remember_state + cfi_restore (t0) + cfi_restore (t1) + cfi_restore (t2) + cfi_restore (t3) + cfi_restore (t4) + 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 $q_low_ret + + .align 4 + cfi_restore_state +$y_is_neg: + /* If we get here, Y is so big that bit 63 is set. The results + from the divide will be completely wrong. Fortunately, the + quotient must be either 0 or 1, so just compute it directly. */ + cmpult Y, X, RV + ldt $f0, 0(sp) + lda sp, FRAME(sp) + cfi_restore ($f0) + cfi_def_cfa_offset (0) + ret $31, (RA), 1 + + cfi_endproc + .size __divqu, .-__divqu + + DO_DIVBYZERO |