/*
* strcmp for ARMv7
*
* Copyright (c) 2012-2022, Arm Limited.
* SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
*/
#if __ARM_ARCH >= 7 && __ARM_ARCH_ISA_ARM >= 1
/* Implementation of strcmp for ARMv7 when DSP instructions are
available. Use ldrd to support wider loads, provided the data
is sufficiently aligned. Use saturating arithmetic to optimize
the compares. */
#include "asmdefs.h"
/* Build Options:
STRCMP_NO_PRECHECK: Don't run a quick pre-check of the first
byte in the string. If comparing completely random strings
the pre-check will save time, since there is a very high
probability of a mismatch in the first character: we save
significant overhead if this is the common case. However,
if strings are likely to be identical (eg because we're
verifying a hit in a hash table), then this check is largely
redundant. */
#define STRCMP_NO_PRECHECK 0
/* Ensure the .cantunwind directive is prepended to .fnend.
Leaf functions cannot throw exceptions - EHABI only supports
synchronous exceptions. */
#define IS_LEAF
/* This version uses Thumb-2 code. */
.thumb
.syntax unified
#ifdef __ARM_BIG_ENDIAN
#define S2LO lsl
#define S2LOEQ lsleq
#define S2HI lsr
#define MSB 0x000000ff
#define LSB 0xff000000
#define BYTE0_OFFSET 24
#define BYTE1_OFFSET 16
#define BYTE2_OFFSET 8
#define BYTE3_OFFSET 0
#else /* not __ARM_BIG_ENDIAN */
#define S2LO lsr
#define S2LOEQ lsreq
#define S2HI lsl
#define BYTE0_OFFSET 0
#define BYTE1_OFFSET 8
#define BYTE2_OFFSET 16
#define BYTE3_OFFSET 24
#define MSB 0xff000000
#define LSB 0x000000ff
#endif /* not __ARM_BIG_ENDIAN */
/* Parameters and result. */
#define src1 r0
#define src2 r1
#define result r0 /* Overlaps src1. */
/* Internal variables. */
#define tmp1 r4
#define tmp2 r5
#define const_m1 r12
/* Additional internal variables for 64-bit aligned data. */
#define data1a r2
#define data1b r3
#define data2a r6
#define data2b r7
#define syndrome_a tmp1
#define syndrome_b tmp2
/* Additional internal variables for 32-bit aligned data. */
#define data1 r2
#define data2 r3
#define syndrome tmp2
/* Macro to compute and return the result value for word-aligned
cases. */
.macro strcmp_epilogue_aligned synd d1 d2 restore_r6
#ifdef __ARM_BIG_ENDIAN
/* If data1 contains a zero byte, then syndrome will contain a 1 in
bit 7 of that byte. Otherwise, the highest set bit in the
syndrome will highlight the first different bit. It is therefore
sufficient to extract the eight bits starting with the syndrome
bit. */
clz tmp1, \synd
lsl r1, \d2, tmp1
.if \restore_r6
ldrd r6, r7, [sp, #8]
.endif
.cfi_restore 6
.cfi_restore 7
lsl \d1, \d1, tmp1
.cfi_remember_state
lsr result, \d1, #24
ldrd r4, r5, [sp], #16
.cfi_restore 4
.cfi_restore 5
.cfi_adjust_cfa_offset -16
sub result, result, r1, lsr #24
epilogue push_ip=HAVE_PAC_LEAF
#else
/* To use the big-endian trick we'd have to reverse all three words.
that's slower than this approach. */
rev \synd, \synd
clz tmp1, \synd
bic tmp1, tmp1, #7
lsr r1, \d2, tmp1
.cfi_remember_state
.if \restore_r6
ldrd r6, r7, [sp, #8]
.endif
.cfi_restore 6
.cfi_restore 7
lsr \d1, \d1, tmp1
and result, \d1, #255
and r1, r1, #255
ldrd r4, r5, [sp], #16
.cfi_restore 4
.cfi_restore 5
.cfi_adjust_cfa_offset -16
sub result, result, r1
epilogue push_ip=HAVE_PAC_LEAF
#endif
.endm
ENTRY(__strcmp_arm)
prologue push_ip=HAVE_PAC_LEAF
#if STRCMP_NO_PRECHECK == 0
ldrb r2, [src1]
ldrb r3, [src2]
cmp r2, #1
it cs
cmpcs r2, r3
bne L(fastpath_exit)
#endif
strd r4, r5, [sp, #-16]!
.cfi_adjust_cfa_offset 16
.cfi_rel_offset 4, 0
.cfi_rel_offset 5, 4
orr tmp1, src1, src2
strd r6, r7, [sp, #8]
.cfi_rel_offset 6, 8
.cfi_rel_offset 7, 12
mvn const_m1, #0
lsl r2, tmp1, #29
cbz r2, L(loop_aligned8)
L(not_aligned):
eor tmp1, src1, src2
tst tmp1, #7
bne L(misaligned8)
/* Deal with mutual misalignment by aligning downwards and then
masking off the unwanted loaded data to prevent a difference. */
and tmp1, src1, #7
bic src1, src1, #7
and tmp2, tmp1, #3
bic src2, src2, #7
lsl tmp2, tmp2, #3 /* Bytes -> bits. */
ldrd data1a, data1b, [src1], #16
tst tmp1, #4
ldrd data2a, data2b, [src2], #16
/* In thumb code we can't use MVN with a register shift, but
we do have ORN. */
S2HI tmp1, const_m1, tmp2
orn data1a, data1a, tmp1
orn data2a, data2a, tmp1
beq L(start_realigned8)
orn data1b, data1b, tmp1
mov data1a, const_m1
orn data2b, data2b, tmp1
mov data2a, const_m1
b L(start_realigned8)
/* Unwind the inner loop by a factor of 2, giving 16 bytes per
pass. */
.p2align 5,,12 /* Don't start in the tail bytes of a cache line. */
.p2align 2 /* Always word aligned. */
L(loop_aligned8):
ldrd data1a, data1b, [src1], #16
ldrd data2a, data2b, [src2], #16
L(start_realigned8):
uadd8 syndrome_b, data1a, const_m1 /* Only want GE bits, */
eor syndrome_a, data1a, data2a
sel syndrome_a, syndrome_a, const_m1
cbnz syndrome_a, L(diff_in_a)
uadd8 syndrome_b, data1b, const_m1 /* Only want GE bits. */
eor syndrome_b, data1b, data2b
sel syndrome_b, syndrome_b, const_m1
cbnz syndrome_b, L(diff_in_b)
ldrd data1a, data1b, [src1, #-8]
ldrd data2a, data2b, [src2, #-8]
uadd8 syndrome_b, data1a, const_m1 /* Only want GE bits, */
eor syndrome_a, data1a, data2a
sel syndrome_a, syndrome_a, const_m1
uadd8 syndrome_b, data1b, const_m1 /* Only want GE bits. */
eor syndrome_b, data1b, data2b
sel syndrome_b, syndrome_b, const_m1
/* Can't use CBZ for backwards branch. */
orrs syndrome_b, syndrome_b, syndrome_a /* Only need if s_a == 0 */
beq L(loop_aligned8)
L(diff_found):
cbnz syndrome_a, L(diff_in_a)
L(diff_in_b):
strcmp_epilogue_aligned syndrome_b, data1b, data2b 1
L(diff_in_a):
.cfi_restore_state
strcmp_epilogue_aligned syndrome_a, data1a, data2a 1
.cfi_restore_state
L(misaligned8):
tst tmp1, #3
bne L(misaligned4)
ands tmp1, src1, #3
bne L(mutual_align4)
/* Unrolled by a factor of 2, to reduce the number of post-increment
operations. */
L(loop_aligned4):
ldr data1, [src1], #8
ldr data2, [src2], #8
L(start_realigned4):
uadd8 syndrome, data1, const_m1 /* Only need GE bits. */
eor syndrome, data1, data2
sel syndrome, syndrome, const_m1
cbnz syndrome, L(aligned4_done)
ldr data1, [src1, #-4]
ldr data2, [src2, #-4]
uadd8 syndrome, data1, const_m1
eor syndrome, data1, data2
sel syndrome, syndrome, const_m1
cmp syndrome, #0
beq L(loop_aligned4)
L(aligned4_done):
strcmp_epilogue_aligned syndrome, data1, data2, 0
L(mutual_align4):
.cfi_restore_state
/* Deal with mutual misalignment by aligning downwards and then
masking off the unwanted loaded data to prevent a difference. */
lsl tmp1, tmp1, #3 /* Bytes -> bits. */
bic src1, src1, #3
ldr data1, [src1], #8
bic src2, src2, #3
ldr data2, [src2], #8
/* In thumb code we can't use MVN with a register shift, but
we do have ORN. */
S2HI tmp1, const_m1, tmp1
orn data1, data1, tmp1
orn data2, data2, tmp1
b L(start_realigned4)
L(misaligned4):
ands tmp1, src1, #3
beq L(src1_aligned)
sub src2, src2, tmp1
bic src1, src1, #3
lsls tmp1, tmp1, #31
ldr data1, [src1], #4
beq L(aligned_m2)
bcs L(aligned_m1)
#if STRCMP_NO_PRECHECK == 1
ldrb data2, [src2, #1]
uxtb tmp1, data1, ror #BYTE1_OFFSET
subs tmp1, tmp1, data2
bne L(misaligned_exit)
cbz data2, L(misaligned_exit)
L(aligned_m2):
ldrb data2, [src2, #2]
uxtb tmp1, data1, ror #BYTE2_OFFSET
subs tmp1, tmp1, data2
bne L(misaligned_exit)
cbz data2, L(misaligned_exit)
L(aligned_m1):
ldrb data2, [src2, #3]
uxtb tmp1, data1, ror #BYTE3_OFFSET
subs tmp1, tmp1, data2
bne L(misaligned_exit)
add src2, src2, #4
cbnz data2, L(src1_aligned)
#else /* STRCMP_NO_PRECHECK */
/* If we've done the pre-check, then we don't need to check the
first byte again here. */
ldrb data2, [src2, #2]
uxtb tmp1, data1, ror #BYTE2_OFFSET
subs tmp1, tmp1, data2
bne L(misaligned_exit)
cbz data2, L(misaligned_exit)
L(aligned_m2):
ldrb data2, [src2, #3]
uxtb tmp1, data1, ror #BYTE3_OFFSET
subs tmp1, tmp1, data2
bne L(misaligned_exit)
cbnz data2, L(aligned_m1)
#endif
L(misaligned_exit):
.cfi_remember_state
mov result, tmp1
ldr r4, [sp], #16
.cfi_restore 4
.cfi_adjust_cfa_offset -16
epilogue push_ip=HAVE_PAC_LEAF
#if STRCMP_NO_PRECHECK == 0
L(fastpath_exit):
.cfi_restore_state
.cfi_remember_state
sub r0, r2, r3
epilogue push_ip=HAVE_PAC_LEAF
L(aligned_m1):
.cfi_restore_state
.cfi_remember_state
add src2, src2, #4
#endif
L(src1_aligned):
.cfi_restore_state
/* src1 is word aligned, but src2 has no common alignment
with it. */
ldr data1, [src1], #4
lsls tmp1, src2, #31 /* C=src2[1], Z=src2[0]. */
bic src2, src2, #3
ldr data2, [src2], #4
bhi L(overlap1) /* C=1, Z=0 => src2[1:0] = 0b11. */
bcs L(overlap2) /* C=1, Z=1 => src2[1:0] = 0b10. */
/* (overlap3) C=0, Z=0 => src2[1:0] = 0b01. */
L(overlap3):
bic tmp1, data1, #MSB
uadd8 syndrome, data1, const_m1
eors syndrome, tmp1, data2, S2LO #8
sel syndrome, syndrome, const_m1
bne 4f
cbnz syndrome, 5f
ldr data2, [src2], #4
eor tmp1, tmp1, data1
cmp tmp1, data2, S2HI #24
bne 6f
ldr data1, [src1], #4
b L(overlap3)
4:
S2LO data2, data2, #8
b L(strcmp_tail)
5:
bics syndrome, syndrome, #MSB
bne L(strcmp_done_equal)
/* We can only get here if the MSB of data1 contains 0, so
fast-path the exit. */
ldrb result, [src2]
.cfi_remember_state
ldrd r4, r5, [sp], #16
.cfi_restore 4
.cfi_restore 5
/* R6/7 Not used in this sequence. */
.cfi_restore 6
.cfi_restore 7
.cfi_adjust_cfa_offset -16
neg result, result
epilogue push_ip=HAVE_PAC_LEAF
6:
.cfi_restore_state
S2LO data1, data1, #24
and data2, data2, #LSB
b L(strcmp_tail)
.p2align 5,,12 /* Ensure at least 3 instructions in cache line. */
L(overlap2):
and tmp1, data1, const_m1, S2LO #16
uadd8 syndrome, data1, const_m1
eors syndrome, tmp1, data2, S2LO #16
sel syndrome, syndrome, const_m1
bne 4f
cbnz syndrome, 5f
ldr data2, [src2], #4
eor tmp1, tmp1, data1
cmp tmp1, data2, S2HI #16
bne 6f
ldr data1, [src1], #4
b L(overlap2)
4:
S2LO data2, data2, #16
b L(strcmp_tail)
5:
ands syndrome, syndrome, const_m1, S2LO #16
bne L(strcmp_done_equal)
ldrh data2, [src2]
S2LO data1, data1, #16
#ifdef __ARM_BIG_ENDIAN
lsl data2, data2, #16
#endif
b L(strcmp_tail)
6:
S2LO data1, data1, #16
and data2, data2, const_m1, S2LO #16
b L(strcmp_tail)
.p2align 5,,12 /* Ensure at least 3 instructions in cache line. */
L(overlap1):
and tmp1, data1, #LSB
uadd8 syndrome, data1, const_m1
eors syndrome, tmp1, data2, S2LO #24
sel syndrome, syndrome, const_m1
bne 4f
cbnz syndrome, 5f
ldr data2, [src2], #4
eor tmp1, tmp1, data1
cmp tmp1, data2, S2HI #8
bne 6f
ldr data1, [src1], #4
b L(overlap1)
4:
S2LO data2, data2, #24
b L(strcmp_tail)
5:
tst syndrome, #LSB
bne L(strcmp_done_equal)
ldr data2, [src2]
6:
S2LO data1, data1, #8
bic data2, data2, #MSB
b L(strcmp_tail)
L(strcmp_done_equal):
mov result, #0
.cfi_remember_state
ldrd r4, r5, [sp], #16
.cfi_restore 4
.cfi_restore 5
/* R6/7 not used in this sequence. */
.cfi_restore 6
.cfi_restore 7
.cfi_adjust_cfa_offset -16
epilogue push_ip=HAVE_PAC_LEAF
L(strcmp_tail):
.cfi_restore_state
#ifndef __ARM_BIG_ENDIAN
rev data1, data1
rev data2, data2
/* Now everything looks big-endian... */
#endif
uadd8 tmp1, data1, const_m1
eor tmp1, data1, data2
sel syndrome, tmp1, const_m1
clz tmp1, syndrome
lsl data1, data1, tmp1
lsl data2, data2, tmp1
lsr result, data1, #24
ldrd r4, r5, [sp], #16
.cfi_restore 4
.cfi_restore 5
/* R6/7 not used in this sequence. */
.cfi_restore 6
.cfi_restore 7
.cfi_adjust_cfa_offset -16
sub result, result, data2, lsr #24
epilogue push_ip=HAVE_PAC_LEAF
END (__strcmp_arm)
#endif /* __ARM_ARCH >= 7 && __ARM_ARCH_ISA_ARM >= 1 */
