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Diffstat (limited to 'rts/gmp/mpn/alpha/cntlz.asm')
| -rw-r--r-- | rts/gmp/mpn/alpha/cntlz.asm | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/rts/gmp/mpn/alpha/cntlz.asm b/rts/gmp/mpn/alpha/cntlz.asm new file mode 100644 index 0000000000..febb3b70d9 --- /dev/null +++ b/rts/gmp/mpn/alpha/cntlz.asm @@ -0,0 +1,68 @@ +dnl Alpha auxiliary for longlong.h's count_leading_zeros + +dnl Copyright (C) 1997, 2000 Free Software Foundation, Inc. + +dnl This file is part of the GNU MP Library. + +dnl The GNU MP Library is free software; you can redistribute it and/or modify +dnl it under the terms of the GNU Lesser General Public License as published by +dnl the Free Software Foundation; either version 2.1 of the License, or (at your +dnl option) any later version. + +dnl The GNU MP Library is distributed in the hope that it will be useful, but +dnl WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +dnl or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public +dnl License for more details. + +dnl You should have received a copy of the GNU Lesser General Public License +dnl along with the GNU MP Library; see the file COPYING.LIB. If not, write to +dnl the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +dnl MA 02111-1307, USA. + +include(`../config.m4') + +dnl DISCUSSION: + +dnl Other methods have been tried, and using a 128-entry table actually trims +dnl about 10% of the execution time (on a 21164) when the table is in the L1 +dnl cache. But under non-benchmarking conditions, the table will hardly be in +dnl the L1 cache. Tricky bit-fiddling methods with multiplies and magic tables +dnl are also possible, but they require many more instructions than the current +dnl code. (But for count_trailing_zeros, such tricks are beneficial.) +dnl Finally, converting to floating-point and extracting the exponent is much +dnl slower. + +ASM_START() +PROLOGUE(MPN(count_leading_zeros)) + bis r31,63,r0 C initialize partial result count + + srl r16,32,r1 C shift down 32 steps -> r1 + cmovne r1,r1,r16 C select r1 if non-zero + cmovne r1,31,r0 C if r1 is nonzero choose smaller count + + srl r16,16,r1 C shift down 16 steps -> r1 + subq r0,16,r2 C generate new partial result count + cmovne r1,r1,r16 C choose new r1 if non-zero + cmovne r1,r2,r0 C choose new count if r1 was non-zero + + srl r16,8,r1 + subq r0,8,r2 + cmovne r1,r1,r16 + cmovne r1,r2,r0 + + srl r16,4,r1 + subq r0,4,r2 + cmovne r1,r1,r16 + cmovne r1,r2,r0 + + srl r16,2,r1 + subq r0,2,r2 + cmovne r1,r1,r16 + cmovne r1,r2,r0 + + srl r16,1,r1 C extract bit 1 + subq r0,r1,r0 C subtract it from partial result + + ret r31,(r26),1 +EPILOGUE(MPN(count_leading_zeros)) +ASM_END() |