arm64/lib/strncmp.S

1 /* SPDX-License-Identifier: GPL-2.0-only */
9  * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
20  *  x0 - const string 1 pointer
21  *  x1 - const string 2 pointer
22  *  x2 - the maximal length to be compared
24  *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
63 	/* Calculate the number of full and partial words -1.  */
72 	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
73 	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
83 	eor	diff, data1, data2  /* Non-zero if differences found.  */
85 	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
96 	lsl	limit, limit, #3    /* Bits -> bytes.  */
121 	neg	tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
125 	/* Big-endian.  Early bytes are at MSB.  */
127 	/* Little-endian.  Early bytes are at LSB.  */
191 	eor	diff, data1, data2  /* Non-zero if differences found.  */
194 	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
214 	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
215 	eor	diff, data1, data2  /* Non-zero if differences found.  */
225 	eor	diff, data1, data2  /* Non-zero if differences found.  */
228 	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
236 	* reversed the byte-order as big-endian,then CLZ can find the most
237 	* significant zero bits.
243 	* For big-endian we cannot use the trick with the syndrome value
244 	* as carry-propagation can corrupt the upper bits if the trailing
256 	/* Re-compute the NUL-byte detection, using a byte-reversed value.*/
264 	* The MS-non-zero bit of the syndrome marks either the first bit
265 	* that is different, or the top bit of the first zero byte.
273 	* But we need to zero-extend (char is unsigned) the value and then
274 	* perform a signed 32-bit subtraction.