1 /* SPDX-License-Identifier: GPL-2.0-only */ <<
2 /* 1 /*
3 * linux/arch/arm/lib/strrchr.S !! 2 * arch/alpha/lib/strrchr.S
>> 3 * Contributed by Richard Henderson (rth@tamu.edu)
4 * 4 *
5 * Copyright (C) 1995-2000 Russell King !! 5 * Return the address of the last occurrence of a given character
6 * !! 6 * within a null-terminated string, or null if it is not found.
7 * ASM optimised string functions <<
8 */ 7 */
9 #include <linux/linkage.h> <<
10 #include <asm/assembler.h> <<
11 8
12 .text !! 9 #include <asm/regdef.h>
13 .align 5 !! 10
14 ENTRY(strrchr) !! 11 .set noreorder
15 mov r3, #0 !! 12 .set noat
16 1: ldrb r2, [r0], #1 !! 13
17 teq r2, r1 !! 14 .align 3
18 subeq r3, r0, #1 !! 15 .ent strrchr
19 teq r2, #0 !! 16 .globl strrchr
20 bne 1b !! 17 strrchr:
21 mov r0, r3 !! 18 .frame sp, 0, ra
22 ret lr !! 19 .prologue 0
23 ENDPROC(strrchr) !! 20
>> 21 zapnot a1, 1, a1 # e0 : zero extend our test character
>> 22 mov zero, t6 # .. e1 : t6 is last match aligned addr
>> 23 sll a1, 8, t5 # e0 : replicate our test character
>> 24 mov zero, t8 # .. e1 : t8 is last match byte compare mask
>> 25 or t5, a1, a1 # e0 :
>> 26 ldq_u t0, 0(a0) # .. e1 : load first quadword
>> 27 sll a1, 16, t5 # e0 :
>> 28 andnot a0, 7, v0 # .. e1 : align source addr
>> 29 or t5, a1, a1 # e0 :
>> 30 lda t4, -1 # .. e1 : build garbage mask
>> 31 sll a1, 32, t5 # e0 :
>> 32 cmpbge zero, t0, t1 # .. e1 : bits set iff byte == zero
>> 33 mskqh t4, a0, t4 # e0 :
>> 34 or t5, a1, a1 # .. e1 : character replication complete
>> 35 xor t0, a1, t2 # e0 : make bytes == c zero
>> 36 cmpbge zero, t4, t4 # .. e1 : bits set iff byte is garbage
>> 37 cmpbge zero, t2, t3 # e0 : bits set iff byte == c
>> 38 andnot t1, t4, t1 # .. e1 : clear garbage from null test
>> 39 andnot t3, t4, t3 # e0 : clear garbage from char test
>> 40 bne t1, $eos # .. e1 : did we already hit the terminator?
>> 41
>> 42 /* Character search main loop */
>> 43 $loop:
>> 44 ldq t0, 8(v0) # e0 : load next quadword
>> 45 cmovne t3, v0, t6 # .. e1 : save previous comparisons match
>> 46 cmovne t3, t3, t8 # e0 :
>> 47 addq v0, 8, v0 # .. e1 :
>> 48 xor t0, a1, t2 # e0 :
>> 49 cmpbge zero, t0, t1 # .. e1 : bits set iff byte == zero
>> 50 cmpbge zero, t2, t3 # e0 : bits set iff byte == c
>> 51 beq t1, $loop # .. e1 : if we havnt seen a null, loop
>> 52
>> 53 /* Mask out character matches after terminator */
>> 54 $eos:
>> 55 negq t1, t4 # e0 : isolate first null byte match
>> 56 and t1, t4, t4 # e1 :
>> 57 subq t4, 1, t5 # e0 : build a mask of the bytes upto...
>> 58 or t4, t5, t4 # e1 : ... and including the null
>> 59
>> 60 and t3, t4, t3 # e0 : mask out char matches after null
>> 61 cmovne t3, t3, t8 # .. e1 : save it, if match found
>> 62 cmovne t3, v0, t6 # e0 :
>> 63
>> 64 /* Locate the address of the last matched character */
>> 65
>> 66 /* Retain the early exit for the ev4 -- the ev5 mispredict penalty
>> 67 is 5 cycles -- the same as just falling through. */
>> 68 beq t8, $retnull # .. e1 :
>> 69
>> 70 and t8, 0xf0, t2 # e0 : binary search for the high bit set
>> 71 cmovne t2, t2, t8 # .. e1 (zdb)
>> 72 cmovne t2, 4, t2 # e0 :
>> 73 and t8, 0xcc, t1 # .. e1 :
>> 74 cmovne t1, t1, t8 # e0 :
>> 75 cmovne t1, 2, t1 # .. e1 :
>> 76 and t8, 0xaa, t0 # e0 :
>> 77 cmovne t0, 1, t0 # .. e1 (zdb)
>> 78 addq t2, t1, t1 # e0 :
>> 79 addq t6, t0, v0 # .. e1 : add our aligned base ptr to the mix
>> 80 addq v0, t1, v0 # e0 :
>> 81 ret # .. e1 :
>> 82
>> 83 $retnull:
>> 84 mov zero, v0 # e0 :
>> 85 ret # .. e1 :
>> 86
>> 87 .end strrchr
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