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Diffstat (limited to 'sysdeps/alpha/bzero.S')
| -rw-r--r-- | sysdeps/alpha/bzero.S | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/sysdeps/alpha/bzero.S b/sysdeps/alpha/bzero.S new file mode 100644 index 0000000000..fffa53d7f1 --- /dev/null +++ b/sysdeps/alpha/bzero.S @@ -0,0 +1,113 @@ +/* Copyright (C) 1996 Free Software Foundation, Inc. + Contributed by Richard Henderson (rth@tamu.edu) + +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 Library General Public License as +published by the Free Software Foundation; either version 2 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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +/* Fill a block of memory with zeros. Optimized for the Alpha architecture: + + - memory accessed as aligned quadwords only + - destination memory not read unless needed for good cache behaviour + - basic blocks arranged to optimize branch prediction for full-quadword + aligned memory blocks. + - partial head and tail quadwords constructed with byte-mask instructions + + This is generally scheduled for the EV5 (got to look out for my own + interests :-), but with EV4 needs in mind. There *should* be no more + stalls for the EV4 than there are for the EV5. +*/ + + +#include <sysdep.h> + + .set noat + .set noreorder + + .text + +/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that + doesn't like putting the entry point for a procedure somewhere in the + middle of the procedure descriptor. Work around this by putting the main + loop in its own procedure descriptor. */ + + /* On entry to this basic block: + t3 == loop counter + t4 == bytes in partial final word + a0 == possibly misaligned destination pointer */ + + .ent bzero_loop + .align 3 +bzero_loop: + .frame sp, 0, ra, 0 + .prologue 0 + + beq t3, $tail # + blbc t3, 0f # skip single store if count even + + stq_u zero, 0(a0) # e0 : store one word + subq t3, 1, t3 # .. e1 : + addq a0, 8, a0 # e0 : + beq t3, $tail # .. e1 : + +0: stq_u zero, 0(a0) # e0 : store two words + subq t3, 2, t3 # .. e1 : + stq_u zero, 8(a0) # e0 : + addq a0, 16, a0 # .. e1 : + bne t3, 0b # e1 : + +$tail: bne t4, 1f # is there a tail to do? + ret # no + +1: ldq_u t0, 0(a0) # yes, load original data + mskqh t0, t4, t0 # + stq_u t0, 0(a0) # + ret # + + .end bzero_loop + +ENTRY(bzero) + .prologue 0 + + mov a0, v0 # e0 : move return value in place + beq a1, $done # .. e1 : early exit for zero-length store + and a0, 7, t1 # e0 : + addq a1, t1, a1 # e1 : add dest misalignment to count + srl a1, 3, t3 # e0 : loop = count >> 3 + and a1, 7, t4 # .. e1 : find number of bytes in tail + unop # : + beq t1, bzero_loop # e1 : aligned head, jump right in + + ldq_u t0, 0(a0) # e0 : load original data to mask into + cmpult a1, 8, t2 # .. e1 : is this a sub-word set? + bne t2, $oneq # e1 : + + mskql t0, a0, t0 # e0 : we span words. finish this partial + subq t3, 1, t3 # e0 : + addq a0, 8, a0 # .. e1 : + stq_u t0, -8(a0) # e0 : + br bzero_loop # .. e1 : + + .align 3 +$oneq: + mskql t0, a0, t2 # e0 : + mskqh t0, a1, t3 # e0 : + or t2, t3, t0 # e1 : + stq_u t0, 0(a0) # e0 : + +$done: ret + + END(bzero) |