arm64/lib/strncmp.S

1 /* SPDX-License-Identifier: GPL-2.0-only */
3  * Copyright (c) 2013-2022, Arm Limited.
6  * https://github.com/ARM-software/optimized-routines/blob/189dfefe37d54c5b/string/aarch64/strncmp.S
14  * ARMv8-a, AArch64.
48 /* Define endian dependent shift operations.
49    On big-endian early bytes are at MSB and on little-endian LSB.
70 	/* NUL detection works on the principle that (X - 1) & (~X) & 0x80
71 	   (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
81 	eor	diff, data1, data2	/* Non-zero if differences found.  */
83 	bics	has_nul, tmp1, tmp2	/* Non-zero if NUL terminator.  */
102 	/* But we need to zero-extend (char is unsigned) the value and then
103 	   perform a signed 32-bit subtraction.  */
114 	lsl	limit, tmp1, #3	/* Bits -> bytes.  */
124 	/* For big-endian we cannot use the trick with the syndrome value
125 	   as carry-propagation can corrupt the upper bits if the trailing
136 	/* Re-compute the NUL-byte detection, using a byte-reversed value.  */
144 	/* The most-significant-non-zero bit of the syndrome marks either the
151 	/* But we need to zero-extend (char is unsigned) the value and then
152 	   perform a signed 32-bit subtraction.  */
167 	neg	tmp3, count, lsl #3	/* 64 - bits(bytes beyond align). */
214 	   The bytes are shown in natural order. For little-endian, it is
235 	mov	mask, -1
249 	orr	data2, data2, tmp1	/* 8 bytes from SRC2 combined from two regs.*/
251 	eor	diff, data1, data2	/* Non-zero if differences found.  */
254 	bic	has_nul, has_nul, tmp3	/* Non-zero if NUL byte found in SRC1. */
263 	/* For big-endian we do a byte reverse to avoid carry-propagation
273 	eor	diff, data2, data1	/* Non-zero if differences found.  */
274 	bic	has_nul, has_nul, tmp3	/* Non-zero if NUL terminator.  */
288 	eor	diff, data2, data1	/* Non-zero if differences found.  */