diff --git a/libc/arch-x86/string/sse2-memrchr-atom.S b/libc/arch-x86/string/sse2-memrchr-atom.S
new file mode 100644
index 0000000..1aa1a1a
--- /dev/null
+++ b/libc/arch-x86/string/sse2-memrchr-atom.S
@@ -0,0 +1,778 @@
+/*
+Copyright (c) 2011, Intel Corporation
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice,
+    * this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above copyright notice,
+    * this list of conditions and the following disclaimer in the documentation
+    * and/or other materials provided with the distribution.
+
+    * Neither the name of Intel Corporation nor the names of its contributors
+    * may be used to endorse or promote products derived from this software
+    * without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, 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.
+*/
+
+#ifndef L
+# define L(label)	.L##label
+#endif
+
+#ifndef cfi_startproc
+# define cfi_startproc	.cfi_startproc
+#endif
+
+#ifndef cfi_endproc
+# define cfi_endproc	.cfi_endproc
+#endif
+
+#ifndef cfi_rel_offset
+# define cfi_rel_offset(reg, off)	.cfi_rel_offset reg, off
+#endif
+
+#ifndef cfi_restore
+# define cfi_restore(reg)	.cfi_restore reg
+#endif
+
+#ifndef cfi_adjust_cfa_offset
+# define cfi_adjust_cfa_offset(off)	.cfi_adjust_cfa_offset off
+#endif
+
+#ifndef ENTRY
+# define ENTRY(name)	\
+	.type name,  @function;	\
+	.globl name;	\
+	.p2align 4;	\
+name:	\
+	cfi_startproc
+#endif
+
+#ifndef END
+# define END(name)	\
+	cfi_endproc;	\
+	.size name,	.-name
+#endif
+
+#define CFI_PUSH(REG)	\
+	cfi_adjust_cfa_offset (4);	\
+	cfi_rel_offset (REG, 0)
+
+#define CFI_POP(REG)	\
+	cfi_adjust_cfa_offset (-4);	\
+	cfi_restore (REG)
+
+#define PUSH(REG) pushl REG; CFI_PUSH (REG)
+#define POP(REG) popl REG; CFI_POP (REG)
+
+#define PARMS  4
+#define STR1  PARMS
+#define STR2  STR1+4
+#define LEN   STR2+4
+
+	.text
+ENTRY (memrchr)
+	mov	STR1(%esp), %ecx
+	movd	STR2(%esp), %xmm1
+	mov	LEN(%esp), %edx
+
+	test	%edx, %edx
+	jz	L(return_null)
+	sub	$16, %edx
+	jbe	L(length_less16)
+
+	punpcklbw %xmm1, %xmm1
+	add	%edx, %ecx
+	punpcklbw %xmm1, %xmm1
+
+	movdqu	(%ecx), %xmm0
+	pshufd	$0, %xmm1, %xmm1
+	pcmpeqb	%xmm1, %xmm0
+
+	pmovmskb %xmm0, %eax
+	test	%eax, %eax
+	jnz	L(exit_dispatch)
+
+	sub	$64, %ecx
+	mov	%ecx, %eax
+	and	$15, %eax
+	jz	L(loop_prolog)
+
+	add	$16, %ecx
+	add	$16, %edx
+	and	$-16, %ecx
+	sub	%eax, %edx
+
+	.p2align 4
+/* Loop start on aligned string.  */
+L(loop_prolog):
+	sub	$64, %edx
+	jbe	L(exit_loop)
+
+	movdqa	48(%ecx), %xmm0
+	pcmpeqb	%xmm1, %xmm0
+	pmovmskb %xmm0, %eax
+	test	%eax, %eax
+	jnz	L(matches48)
+
+	movdqa	32(%ecx), %xmm2
+	pcmpeqb	%xmm1, %xmm2
+	pmovmskb %xmm2, %eax
+	test	%eax, %eax
+	jnz	L(matches32)
+
+	movdqa	16(%ecx), %xmm3
+	pcmpeqb	%xmm1, %xmm3
+	pmovmskb %xmm3, %eax
+	test	%eax, %eax
+	jnz	L(matches16)
+
+	movdqa	(%ecx), %xmm4
+	pcmpeqb	%xmm1, %xmm4
+	pmovmskb %xmm4, %eax
+	test	%eax, %eax
+	jnz	L(exit_dispatch)
+
+	sub	$64, %ecx
+	sub	$64, %edx
+	jbe	L(exit_loop)
+
+	movdqa	48(%ecx), %xmm0
+	pcmpeqb	%xmm1, %xmm0
+	pmovmskb %xmm0, %eax
+	test	%eax, %eax
+	jnz	L(matches48)
+
+	movdqa	32(%ecx), %xmm2
+	pcmpeqb	%xmm1, %xmm2
+	pmovmskb %xmm2, %eax
+	test	%eax, %eax
+	jnz	L(matches32)
+
+	movdqa	16(%ecx), %xmm3
+	pcmpeqb	%xmm1, %xmm3
+	pmovmskb %xmm3, %eax
+	test	%eax, %eax
+	jnz	L(matches16)
+
+	movdqa	(%ecx), %xmm3
+	pcmpeqb	%xmm1, %xmm3
+	pmovmskb %xmm3, %eax
+	test	%eax, %eax
+	jnz	L(exit_dispatch)
+
+	mov	%ecx, %eax
+	and	$63, %eax
+	test	%eax, %eax
+	jz	L(align64_loop)
+
+	add	$64, %ecx
+	add	$64, %edx
+	and	$-64, %ecx
+	sub	%eax, %edx
+
+	.p2align 4
+L(align64_loop):
+	sub	$64, %ecx
+	sub	$64, %edx
+	jbe	L(exit_loop)
+
+	movdqa	(%ecx), %xmm0
+	movdqa	16(%ecx), %xmm2
+	movdqa	32(%ecx), %xmm3
+	movdqa	48(%ecx), %xmm4
+
+	pcmpeqb	%xmm1, %xmm0
+	pcmpeqb	%xmm1, %xmm2
+	pcmpeqb	%xmm1, %xmm3
+	pcmpeqb	%xmm1, %xmm4
+
+	pmaxub	%xmm3, %xmm0
+	pmaxub	%xmm4, %xmm2
+	pmaxub	%xmm0, %xmm2
+	pmovmskb %xmm2, %eax
+
+	test	%eax, %eax
+	jz	L(align64_loop)
+
+	pmovmskb %xmm4, %eax
+	test	%eax, %eax
+	jnz	L(matches48)
+
+	pmovmskb %xmm3, %eax
+	test	%eax, %eax
+	jnz	L(matches32)
+
+	movdqa	16(%ecx), %xmm2
+
+	pcmpeqb	%xmm1, %xmm2
+	pcmpeqb	(%ecx), %xmm1
+
+	pmovmskb %xmm2, %eax
+	test	%eax, %eax
+	jnz	L(matches16)
+
+	pmovmskb %xmm1, %eax
+	test	%ah, %ah
+	jnz	L(exit_dispatch_high)
+	mov	%al, %dl
+	and	$15 << 4, %dl
+	jnz	L(exit_dispatch_8)
+	test	$0x08, %al
+	jnz	L(exit_4)
+	test	$0x04, %al
+	jnz	L(exit_3)
+	test	$0x02, %al
+	jnz	L(exit_2)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(exit_loop):
+	add	$64, %edx
+	cmp	$32, %edx
+	jbe	L(exit_loop_32)
+
+	movdqa	48(%ecx), %xmm0
+	pcmpeqb	%xmm1, %xmm0
+	pmovmskb %xmm0, %eax
+	test	%eax, %eax
+	jnz	L(matches48)
+
+	movdqa	32(%ecx), %xmm2
+	pcmpeqb	%xmm1, %xmm2
+	pmovmskb %xmm2, %eax
+	test	%eax, %eax
+	jnz	L(matches32)
+
+	movdqa	16(%ecx), %xmm3
+	pcmpeqb	%xmm1, %xmm3
+	pmovmskb %xmm3, %eax
+	test	%eax, %eax
+	jnz	L(matches16_1)
+	cmp	$48, %edx
+	jbe	L(return_null)
+
+	pcmpeqb	(%ecx), %xmm1
+	pmovmskb %xmm1, %eax
+	test	%eax, %eax
+	jnz	L(matches0_1)
+	xor	%eax, %eax
+	ret
+
+	.p2align 4
+L(exit_loop_32):
+	movdqa	48(%ecx), %xmm0
+	pcmpeqb	%xmm1, %xmm0
+	pmovmskb %xmm0, %eax
+	test	%eax, %eax
+	jnz	L(matches48_1)
+	cmp	$16, %edx
+	jbe	L(return_null)
+
+	pcmpeqb	32(%ecx), %xmm1
+	pmovmskb %xmm1, %eax
+	test	%eax, %eax
+	jnz	L(matches32_1)
+	xor	%eax, %eax
+	ret
+
+	.p2align 4
+L(matches16):
+	lea	16(%ecx), %ecx
+	test	%ah, %ah
+	jnz	L(exit_dispatch_high)
+	mov	%al, %dl
+	and	$15 << 4, %dl
+	jnz	L(exit_dispatch_8)
+	test	$0x08, %al
+	jnz	L(exit_4)
+	test	$0x04, %al
+	jnz	L(exit_3)
+	test	$0x02, %al
+	jnz	L(exit_2)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(matches32):
+	lea	32(%ecx), %ecx
+	test	%ah, %ah
+	jnz	L(exit_dispatch_high)
+	mov	%al, %dl
+	and	$15 << 4, %dl
+	jnz	L(exit_dispatch_8)
+	test	$0x08, %al
+	jnz	L(exit_4)
+	test	$0x04, %al
+	jnz	L(exit_3)
+	test	$0x02, %al
+	jnz	L(exit_2)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(matches48):
+	lea	48(%ecx), %ecx
+
+	.p2align 4
+L(exit_dispatch):
+	test	%ah, %ah
+	jnz	L(exit_dispatch_high)
+	mov	%al, %dl
+	and	$15 << 4, %dl
+	jnz	L(exit_dispatch_8)
+	test	$0x08, %al
+	jnz	L(exit_4)
+	test	$0x04, %al
+	jnz	L(exit_3)
+	test	$0x02, %al
+	jnz	L(exit_2)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_8):
+	test	$0x80, %al
+	jnz	L(exit_8)
+	test	$0x40, %al
+	jnz	L(exit_7)
+	test	$0x20, %al
+	jnz	L(exit_6)
+	lea	4(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_high):
+	mov	%ah, %dh
+	and	$15 << 4, %dh
+	jnz	L(exit_dispatch_high_8)
+	test	$0x08, %ah
+	jnz	L(exit_12)
+	test	$0x04, %ah
+	jnz	L(exit_11)
+	test	$0x02, %ah
+	jnz	L(exit_10)
+	lea	8(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_high_8):
+	test	$0x80, %ah
+	jnz	L(exit_16)
+	test	$0x40, %ah
+	jnz	L(exit_15)
+	test	$0x20, %ah
+	jnz	L(exit_14)
+	lea	12(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_2):
+	lea	1(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_3):
+	lea	2(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_4):
+	lea	3(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_6):
+	lea	5(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_7):
+	lea	6(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_8):
+	lea	7(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_10):
+	lea	9(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_11):
+	lea	10(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_12):
+	lea	11(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_14):
+	lea	13(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_15):
+	lea	14(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_16):
+	lea	15(%ecx), %eax
+	ret
+
+	.p2align 4
+L(matches0_1):
+	lea	-64(%edx), %edx
+
+	test	%ah, %ah
+	jnz	L(exit_dispatch_1_high)
+	mov	%al, %ah
+	and	$15 << 4, %ah
+	jnz	L(exit_dispatch_1_8)
+	test	$0x08, %al
+	jnz	L(exit_1_4)
+	test	$0x04, %al
+	jnz	L(exit_1_3)
+	test	$0x02, %al
+	jnz	L(exit_1_2)
+
+	add	$0, %edx
+	jl	L(return_null)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(matches16_1):
+	lea	-48(%edx), %edx
+	lea	16(%ecx), %ecx
+
+	test	%ah, %ah
+	jnz	L(exit_dispatch_1_high)
+	mov	%al, %ah
+	and	$15 << 4, %ah
+	jnz	L(exit_dispatch_1_8)
+	test	$0x08, %al
+	jnz	L(exit_1_4)
+	test	$0x04, %al
+	jnz	L(exit_1_3)
+	test	$0x02, %al
+	jnz	L(exit_1_2)
+
+	add	$0, %edx
+	jl	L(return_null)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(matches32_1):
+	lea	-32(%edx), %edx
+	lea	32(%ecx), %ecx
+
+	test	%ah, %ah
+	jnz	L(exit_dispatch_1_high)
+	mov	%al, %ah
+	and	$15 << 4, %ah
+	jnz	L(exit_dispatch_1_8)
+	test	$0x08, %al
+	jnz	L(exit_1_4)
+	test	$0x04, %al
+	jnz	L(exit_1_3)
+	test	$0x02, %al
+	jnz	L(exit_1_2)
+
+	add	$0, %edx
+	jl	L(return_null)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(matches48_1):
+	lea	-16(%edx), %edx
+	lea	48(%ecx), %ecx
+
+	.p2align 4
+L(exit_dispatch_1):
+	test	%ah, %ah
+	jnz	L(exit_dispatch_1_high)
+	mov	%al, %ah
+	and	$15 << 4, %ah
+	jnz	L(exit_dispatch_1_8)
+	test	$0x08, %al
+	jnz	L(exit_1_4)
+	test	$0x04, %al
+	jnz	L(exit_1_3)
+	test	$0x02, %al
+	jnz	L(exit_1_2)
+
+	add	$0, %edx
+	jl	L(return_null)
+	mov	%ecx, %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_1_8):
+	test	$0x80, %al
+	jnz	L(exit_1_8)
+	test	$0x40, %al
+	jnz	L(exit_1_7)
+	test	$0x20, %al
+	jnz	L(exit_1_6)
+
+	add	$4, %edx
+	jl	L(return_null)
+	lea	4(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_1_high):
+	mov	%ah, %al
+	and	$15 << 4, %al
+	jnz	L(exit_dispatch_1_high_8)
+	test	$0x08, %ah
+	jnz	L(exit_1_12)
+	test	$0x04, %ah
+	jnz	L(exit_1_11)
+	test	$0x02, %ah
+	jnz	L(exit_1_10)
+
+	add	$8, %edx
+	jl	L(return_null)
+	lea	8(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_dispatch_1_high_8):
+	test	$0x80, %ah
+	jnz	L(exit_1_16)
+	test	$0x40, %ah
+	jnz	L(exit_1_15)
+	test	$0x20, %ah
+	jnz	L(exit_1_14)
+
+	add	$12, %edx
+	jl	L(return_null)
+	lea	12(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_2):
+	add	$1, %edx
+	jl	L(return_null)
+	lea	1(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_3):
+	add	$2, %edx
+	jl	L(return_null)
+	lea	2(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_4):
+	add	$3, %edx
+	jl	L(return_null)
+	lea	3(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_6):
+	add	$5, %edx
+	jl	L(return_null)
+	lea	5(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_7):
+	add	$6, %edx
+	jl	L(return_null)
+	lea	6(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_8):
+	add	$7, %edx
+	jl	L(return_null)
+	lea	7(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_10):
+	add	$9, %edx
+	jl	L(return_null)
+	lea	9(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_11):
+	add	$10, %edx
+	jl	L(return_null)
+	lea	10(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_12):
+	add	$11, %edx
+	jl	L(return_null)
+	lea	11(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_14):
+	add	$13, %edx
+	jl	L(return_null)
+	lea	13(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_15):
+	add	$14, %edx
+	jl	L(return_null)
+	lea	14(%ecx), %eax
+	ret
+
+	.p2align 4
+L(exit_1_16):
+	add	$15, %edx
+	jl	L(return_null)
+	lea	15(%ecx), %eax
+	ret
+
+	.p2align 4
+L(return_null):
+	xor	%eax, %eax
+	ret
+
+	.p2align 4
+L(length_less16_offset0):
+	mov	%dl, %cl
+	pcmpeqb	(%eax), %xmm1
+
+	mov	$1, %edx
+	sal	%cl, %edx
+	sub	$1, %edx
+
+	mov	%eax, %ecx
+	pmovmskb %xmm1, %eax
+
+	and	%edx, %eax
+	test	%eax, %eax
+	jnz	L(exit_dispatch)
+
+	xor	%eax, %eax
+	ret
+
+	.p2align 4
+L(length_less16):
+	punpcklbw %xmm1, %xmm1
+	add	$16, %edx
+	punpcklbw %xmm1, %xmm1
+
+	mov	%ecx, %eax
+	pshufd	$0, %xmm1, %xmm1
+
+	and	$15, %ecx
+	jz	L(length_less16_offset0)
+
+	PUSH	(%edi)
+
+	mov	%cl, %dh
+	add	%dl, %dh
+	and	$-16, %eax
+
+	sub	$16, %dh
+	ja	L(length_less16_part2)
+
+	pcmpeqb	(%eax), %xmm1
+	pmovmskb %xmm1, %edi
+
+	sar	%cl, %edi
+	add	%ecx, %eax
+	mov	%dl, %cl
+
+	mov	$1, %edx
+	sal	%cl, %edx
+	sub	$1, %edx
+
+	and	%edx, %edi
+	test	%edi, %edi
+	jz	L(ret_null)
+
+	bsr	%edi, %edi
+	add	%edi, %eax
+	POP	(%edi)
+	ret
+
+	CFI_PUSH     (%edi)
+
+	.p2align 4
+L(length_less16_part2):
+	movdqa	16(%eax), %xmm2
+	pcmpeqb	%xmm1, %xmm2
+	pmovmskb %xmm2, %edi
+
+	mov	%cl, %ch
+
+	mov	%dh, %cl
+	mov	$1, %edx
+	sal	%cl, %edx
+	sub	$1, %edx
+
+	and	%edx, %edi
+
+	test	%edi, %edi
+	jnz	L(length_less16_part2_return)
+
+	pcmpeqb	(%eax), %xmm1
+	pmovmskb %xmm1, %edi
+
+	mov	%ch, %cl
+	sar	%cl, %edi
+	test	%edi, %edi
+	jz	L(ret_null)
+
+	bsr	%edi, %edi
+	add	%edi, %eax
+	xor	%ch, %ch
+	add	%ecx, %eax
+	POP	(%edi)
+	ret
+
+	CFI_PUSH     (%edi)
+
+	.p2align 4
+L(length_less16_part2_return):
+	bsr	%edi, %edi
+	lea	16(%eax, %edi), %eax
+	POP	(%edi)
+	ret
+
+	CFI_PUSH     (%edi)
+
+	.p2align 4
+L(ret_null):
+	xor	%eax, %eax
+	POP	(%edi)
+	ret
+
+END (memrchr)