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Diffstat (limited to 'sysdeps/alpha/strncmp.S')
| -rw-r--r-- | sysdeps/alpha/strncmp.S | 277 |
1 files changed, 277 insertions, 0 deletions
diff --git a/sysdeps/alpha/strncmp.S b/sysdeps/alpha/strncmp.S new file mode 100644 index 0000000000..10a8f5c20c --- /dev/null +++ b/sysdeps/alpha/strncmp.S @@ -0,0 +1,277 @@ +/* Copyright (C) 1996-2014 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 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/>. */ + +/* Bytewise compare two null-terminated strings of length no longer than N. */ + +#include <sysdep.h> + + .set noat + .set noreorder + +/* EV6 only predicts one branch per octaword. We'll use these to push + subsequent branches back to the next bundle. This will generally add + a fetch+decode cycle to older machines, so skip in that case. */ +#ifdef __alpha_fix__ +# define ev6_unop unop +#else +# define ev6_unop +#endif + + .text + +ENTRY(strncmp) +#ifdef PROF + ldgp gp, 0(pv) + lda AT, _mcount + jsr AT, (AT), _mcount + .prologue 1 +#else + .prologue 0 +#endif + + xor a0, a1, t2 # are s1 and s2 co-aligned? + beq a2, $zerolength + ldq_u t0, 0(a0) # load asap to give cache time to catch up + ldq_u t1, 0(a1) + lda t3, -1 + and t2, 7, t2 + srl t3, 1, t6 + and a0, 7, t4 # find s1 misalignment + and a1, 7, t5 # find s2 misalignment + cmovlt a2, t6, a2 # bound neg count to LONG_MAX + addq a1, a2, a3 # s2+count + addq a2, t4, a2 # bias count by s1 misalignment + and a2, 7, t10 # ofs of last byte in s1 last word + srl a2, 3, a2 # remaining full words in s1 count + bne t2, $unaligned + + /* On entry to this basic block: + t0 == the first word of s1. + t1 == the first word of s2. + t3 == -1. */ +$aligned: + mskqh t3, a1, t8 # mask off leading garbage + ornot t1, t8, t1 + ornot t0, t8, t0 + cmpbge zero, t1, t7 # bits set iff null found + beq a2, $eoc # check end of count + bne t7, $eos + beq t10, $ant_loop + + /* Aligned compare main loop. + On entry to this basic block: + t0 == an s1 word. + t1 == an s2 word not containing a null. */ + + .align 4 +$a_loop: + xor t0, t1, t2 # e0 : + bne t2, $wordcmp # .. e1 (zdb) + ldq_u t1, 8(a1) # e0 : + ldq_u t0, 8(a0) # .. e1 : + + subq a2, 1, a2 # e0 : + addq a1, 8, a1 # .. e1 : + addq a0, 8, a0 # e0 : + beq a2, $eoc # .. e1 : + + cmpbge zero, t1, t7 # e0 : + beq t7, $a_loop # .. e1 : + + br $eos + + /* Alternate aligned compare loop, for when there's no trailing + bytes on the count. We have to avoid reading too much data. */ + .align 4 +$ant_loop: + xor t0, t1, t2 # e0 : + ev6_unop + ev6_unop + bne t2, $wordcmp # .. e1 (zdb) + + subq a2, 1, a2 # e0 : + beq a2, $zerolength # .. e1 : + ldq_u t1, 8(a1) # e0 : + ldq_u t0, 8(a0) # .. e1 : + + addq a1, 8, a1 # e0 : + addq a0, 8, a0 # .. e1 : + cmpbge zero, t1, t7 # e0 : + beq t7, $ant_loop # .. e1 : + + br $eos + + /* The two strings are not co-aligned. Align s1 and cope. */ + /* On entry to this basic block: + t0 == the first word of s1. + t1 == the first word of s2. + t3 == -1. + t4 == misalignment of s1. + t5 == misalignment of s2. + t10 == misalignment of s1 end. */ + .align 4 +$unaligned: + /* If s1 misalignment is larger than s2 misalignment, we need + extra startup checks to avoid SEGV. */ + subq a1, t4, a1 # adjust s2 for s1 misalignment + cmpult t4, t5, t9 + subq a3, 1, a3 # last byte of s2 + bic a1, 7, t8 + mskqh t3, t5, t7 # mask garbage in s2 + subq a3, t8, a3 + ornot t1, t7, t7 + srl a3, 3, a3 # remaining full words in s2 count + beq t9, $u_head + + /* Failing that, we need to look for both eos and eoc within the + first word of s2. If we find either, we can continue by + pretending that the next word of s2 is all zeros. */ + lda t2, 0 # next = zero + cmpeq a3, 0, t8 # eoc in the first word of s2? + cmpbge zero, t7, t7 # eos in the first word of s2? + or t7, t8, t8 + bne t8, $u_head_nl + + /* We know just enough now to be able to assemble the first + full word of s2. We can still find a zero at the end of it. + + On entry to this basic block: + t0 == first word of s1 + t1 == first partial word of s2. + t3 == -1. + t10 == ofs of last byte in s1 last word. + t11 == ofs of last byte in s2 last word. */ +$u_head: + ldq_u t2, 8(a1) # load second partial s2 word + subq a3, 1, a3 +$u_head_nl: + extql t1, a1, t1 # create first s2 word + mskqh t3, a0, t8 + extqh t2, a1, t4 + ornot t0, t8, t0 # kill s1 garbage + or t1, t4, t1 # s2 word now complete + cmpbge zero, t0, t7 # find eos in first s1 word + ornot t1, t8, t1 # kill s2 garbage + beq a2, $eoc + subq a2, 1, a2 + bne t7, $eos + mskql t3, a1, t8 # mask out s2[1] bits we have seen + xor t0, t1, t4 # compare aligned words + or t2, t8, t8 + bne t4, $wordcmp + cmpbge zero, t8, t7 # eos in high bits of s2[1]? + cmpeq a3, 0, t8 # eoc in s2[1]? + or t7, t8, t7 + bne t7, $u_final + + /* Unaligned copy main loop. In order to avoid reading too much, + the loop is structured to detect zeros in aligned words from s2. + This has, unfortunately, effectively pulled half of a loop + iteration out into the head and half into the tail, but it does + prevent nastiness from accumulating in the very thing we want + to run as fast as possible. + + On entry to this basic block: + t2 == the unshifted low-bits from the next s2 word. + t10 == ofs of last byte in s1 last word. + t11 == ofs of last byte in s2 last word. */ + .align 4 +$u_loop: + extql t2, a1, t3 # e0 : + ldq_u t2, 16(a1) # .. e1 : load next s2 high bits + ldq_u t0, 8(a0) # e0 : load next s1 word + addq a1, 8, a1 # .. e1 : + + addq a0, 8, a0 # e0 : + subq a3, 1, a3 # .. e1 : + extqh t2, a1, t1 # e0 : + cmpbge zero, t0, t7 # .. e1 : eos in current s1 word + + or t1, t3, t1 # e0 : + beq a2, $eoc # .. e1 : eoc in current s1 word + subq a2, 1, a2 # e0 : + cmpbge zero, t2, t4 # .. e1 : eos in s2[1] + + xor t0, t1, t3 # e0 : compare the words + ev6_unop + ev6_unop + bne t7, $eos # .. e1 : + + cmpeq a3, 0, t5 # e0 : eoc in s2[1] + ev6_unop + ev6_unop + bne t3, $wordcmp # .. e1 : + + or t4, t5, t4 # e0 : eos or eoc in s2[1]. + beq t4, $u_loop # .. e1 (zdb) + + /* We've found a zero in the low bits of the last s2 word. Get + the next s1 word and align them. */ + .align 3 +$u_final: + ldq_u t0, 8(a0) + extql t2, a1, t1 + cmpbge zero, t1, t7 + bne a2, $eos + + /* We've hit end of count. Zero everything after the count + and compare whats left. */ + .align 3 +$eoc: + mskql t0, t10, t0 + mskql t1, t10, t1 + cmpbge zero, t1, t7 + + /* We've found a zero somewhere in a word we just read. + On entry to this basic block: + t0 == s1 word + t1 == s2 word + t7 == cmpbge mask containing the zero. */ + .align 3 +$eos: + negq t7, t6 # create bytemask of valid data + and t6, t7, t8 + subq t8, 1, t6 + or t6, t8, t7 + zapnot t0, t7, t0 # kill the garbage + zapnot t1, t7, t1 + xor t0, t1, v0 # ... and compare + beq v0, $done + + /* Here we have two differing co-aligned words in t0 & t1. + Bytewise compare them and return (t0 > t1 ? 1 : -1). */ + .align 3 +$wordcmp: + cmpbge t0, t1, t2 # comparison yields bit mask of ge + cmpbge t1, t0, t3 + xor t2, t3, t0 # bits set iff t0/t1 bytes differ + negq t0, t1 # clear all but least bit + and t0, t1, t0 + lda v0, -1 + and t0, t2, t1 # was bit set in t0 > t1? + cmovne t1, 1, v0 +$done: + ret + + .align 3 +$zerolength: + clr v0 + ret + + END(strncmp) +libc_hidden_builtin_def (strncmp) |