bionic: Use a more simple strrchr for arm64

 * Current version seems like overkill, and it doesn't compile with
   Clang. Use a simplified version from ARM.

Change-Id: I2fe5467b6a504ea04b5f28a08d92e7c2306772d0

1 files changed, 21 insertions, 138 deletions

diff --git a/libc/arch-arm64/generic/bionic/strrchr.S b/libc/arch-arm64/generic/bionic/strrchr.S
index 46b50312f..409bc7191 100644
--- a/libc/arch-arm64/generic/bionic/strrchr.S
+++ b/libc/arch-arm64/generic/bionic/strrchr.S
@@ -25,147 +25,30 @@
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  */
-
-/* Assumptions:
- *
- * ARMv8-a, AArch64
- * Neon Available.
- */
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+   
+*/
 
 #include <private/bionic_asm.h>
 
-/* Arguments and results.  */
-#define srcin		x0
-#define chrin		w1
-
-#define result		x0
-
-#define src		x2
-#define	tmp1		x3
-#define wtmp2		w4
-#define tmp3		x5
-#define src_match	x6
-#define src_offset	x7
-#define const_m1	x8
-#define tmp4		x9
-#define nul_match	x10
-#define chr_match	x11
-
-#define vrepchr		v0
-#define vdata1		v1
-#define vdata2		v2
-#define vhas_nul1	v3
-#define vhas_nul2	v4
-#define vhas_chr1	v5
-#define vhas_chr2	v6
-#define vrepmask_0	v7
-#define vrepmask_c	v16
-#define vend1		v17
-#define vend2		v18
-
-/* Core algorithm.
-
-   For each 32-byte hunk we calculate a 64-bit syndrome value, with
-   two bits per byte (LSB is always in bits 0 and 1, for both big
-   and little-endian systems).  For each tuple, bit 0 is set iff
-   the relevant byte matched the requested character; bit 1 is set
-   iff the relevant byte matched the NUL end of string (we trigger
-   off bit0 for the special case of looking for NUL).  Since the bits
-   in the syndrome reflect exactly the order in which things occur
-   in the original string a count_trailing_zeros() operation will
-   identify exactly which byte is causing the termination, and why.  */
-
-/* Locals and temporaries.  */
-
+/*
+ * Find the last occurrence of a character in a string.
+ *
+ * Parameters:
+ *	x0 - str
+ *	x1 - c
+ * Returns:
+ *	x0 - address of last occurrence of 'c' or 0
+ */
 ENTRY(strrchr)
-	/* Magic constant 0x40100401 to allow us to identify which lane
-	   matches the requested byte.  Magic constant 0x80200802 used
-	   similarly for NUL termination.  */
-	mov	wtmp2, #0x0401
-	movk	wtmp2, #0x4010, lsl #16
-	dup	vrepchr.16b, chrin
-	bic	src, srcin, #31		/* Work with aligned 32-byte hunks.  */
-	dup	vrepmask_c.4s, wtmp2
-	mov	src_offset, #0
-	ands	tmp1, srcin, #31
-	add	vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
-	b.eq	.Laligned
-
-	/* Input string is not 32-byte aligned.  Rather than forcing
-	   the padding bytes to a safe value, we calculate the syndrome
-	   for all the bytes, but then mask off those bits of the
-	   syndrome that are related to the padding.  */
-	ld1	{vdata1.16b, vdata2.16b}, [src], #32
-	neg	tmp1, tmp1
-	cmeq	vhas_nul1.16b, vdata1.16b, #0
-	cmeq	vhas_chr1.16b, vdata1.16b, vrepchr.16b
-	cmeq	vhas_nul2.16b, vdata2.16b, #0
-	cmeq	vhas_chr2.16b, vdata2.16b, vrepchr.16b
-	and	vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
-	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
-	and	vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
-	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
-	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b	// 256->128
-	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b	// 256->128
-	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b	// 128->64
-	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b	// 128->64
-	mov	nul_match, vhas_nul1.2d[0]
-	lsl	tmp1, tmp1, #1
-	mov	const_m1, #~0
-	mov	chr_match, vhas_chr1.2d[0]
-	lsr	tmp3, const_m1, tmp1
-
-	bic	nul_match, nul_match, tmp3	// Mask padding bits.
-	bic	chr_match, chr_match, tmp3	// Mask padding bits.
-	cbnz	nul_match, .Ltail
-
-.Lloop:
-	cmp	chr_match, #0
-	csel	src_match, src, src_match, ne
-	csel	src_offset, chr_match, src_offset, ne
-.Laligned:
-	ld1	{vdata1.16b, vdata2.16b}, [src], #32
-	cmeq	vhas_nul1.16b, vdata1.16b, #0
-	cmeq	vhas_chr1.16b, vdata1.16b, vrepchr.16b
-	cmeq	vhas_nul2.16b, vdata2.16b, #0
-	cmeq	vhas_chr2.16b, vdata2.16b, vrepchr.16b
-	addp	vend1.16b, vhas_nul1.16b, vhas_nul2.16b	// 256->128
-	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
-	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
-	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b	// 256->128
-	addp	vend1.16b, vend1.16b, vend1.16b	// 128->64
-	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b	// 128->64
-	mov	nul_match, vend1.2d[0]
-	mov	chr_match, vhas_chr1.2d[0]
-	cbz	nul_match, .Lloop
-
-	and	vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
-	and	vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
-	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
-	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
-	mov	nul_match, vhas_nul1.2d[0]
-
-.Ltail:
-	/* Work out exactly where the string ends.  */
-	sub	tmp4, nul_match, #1
-	eor	tmp4, tmp4, nul_match
-	ands	chr_match, chr_match, tmp4
-	/* And pick the values corresponding to the last match.  */
-	csel	src_match, src, src_match, ne
-	csel	src_offset, chr_match, src_offset, ne
-
-	/* Count down from the top of the syndrome to find the last match.  */
-	clz	tmp3, src_offset
-	/* Src_match points beyond the word containing the match, so we can
-	   simply subtract half the bit-offset into the syndrome.  Because
-	   we are counting down, we need to go back one more character.  */
-	add	tmp3, tmp3, #2
-	sub	result, src_match, tmp3, lsr #1
-	/* But if the syndrome shows no match was found, then return NULL.  */
-	cmp	src_offset, #0
-	csel	result, result, xzr, ne
-
+	mov	x3, #0
+	and	w1, w1, #0xff
+1:	ldrb	w2, [x0], #1
+	cbz	w2, 2f
+	cmp	w2, w1
+	b.ne	1b
+	sub	x3, x0, #1
+	b	1b
+2:	mov	x0, x3
 	ret
-
 END(strrchr)