/* Optimized strncmp implementation for PowerPC64/POWER10.
   Copyright (C) 2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>

/* Implements the function

   int [r3] strncmp (const char *s1 [r3], const char *s2 [r4], size_t [r5] n)

   The implementation uses unaligned doubleword access to avoid specialized
   code paths depending of data alignment for first 32 bytes and uses
   vectorised loops after that.  */

#ifndef STRNCMP
# define STRNCMP strncmp
#endif

/* TODO: Change this to actual instructions when minimum binutils is upgraded
   to 2.27.  Macros are defined below for these newer instructions in order
   to maintain compatibility.  */

#define LXVP(xtp,dq,ra)              \
	.long(((6)<<(32-6))          \
	| ((((xtp)-32)>>1)<<(32-10)) \
	| ((1)<<(32-11))             \
	| ((ra)<<(32-16))            \
	| dq)

#define COMPARE_16(vreg1,vreg2,offset) \
	lxv	  vreg1+32,offset(r3); \
	lxv	  vreg2+32,offset(r4); \
	vcmpnezb. v7,vreg1,vreg2;      \
	bne	  cr6,L(different);    \
	cmpldi	  cr7,r5,16;           \
	ble	  cr7,L(ret0);         \
	addi	  r5,r5,-16;

#define COMPARE_32(vreg1,vreg2,offset,label1,label2) \
	LXVP(vreg1+32,offset,r3);                    \
	LXVP(vreg2+32,offset,r4);                    \
	vcmpnezb. v7,vreg1+1,vreg2+1;                \
	bne	  cr6,L(label1);                     \
	vcmpnezb. v7,vreg1,vreg2;                    \
	bne	  cr6,L(label2);                     \
	cmpldi	  cr7,r5,32;                         \
	ble	  cr7,L(ret0);                       \
	addi	  r5,r5,-32;

#define TAIL_FIRST_16B(vreg1,vreg2) \
	vctzlsbb r6,v7;             \
	cmpld	 cr7,r5,r6;         \
	ble	 cr7,L(ret0);       \
	vextubrx r5,r6,vreg1;       \
	vextubrx r4,r6,vreg2;       \
	subf	 r3,r4,r5;          \
	blr;

#define TAIL_SECOND_16B(vreg1,vreg2) \
	vctzlsbb r6,v7;              \
	addi	 r0,r6,16;           \
	cmpld	 cr7,r5,r0;          \
	ble	 cr7,L(ret0);        \
	vextubrx r5,r6,vreg1;        \
	vextubrx r4,r6,vreg2;        \
	subf	 r3,r4,r5;           \
	blr;

#define CHECK_N_BYTES(reg1,reg2,len_reg) \
	sldi	  r6,len_reg,56;	 \
	lxvl	  32+v4,reg1,r6;	 \
	lxvl	  32+v5,reg2,r6;	 \
	add	  reg1,reg1,len_reg;	 \
	add	  reg2,reg2,len_reg;	 \
	vcmpnezb  v7,v4,v5;		 \
	vctzlsbb  r6,v7;		 \
	cmpld	  cr7,r6,len_reg;	 \
	blt	  cr7,L(different);	 \
	cmpld	  cr7,r5,len_reg;	 \
	ble	  cr7,L(ret0);		 \
	sub	  r5,r5,len_reg;	 \

	/* TODO: change this to .machine power10 when the minimum required
	 binutils allows it.  */
	.machine  power9
ENTRY_TOCLESS (STRNCMP, 4)
	/* Check if size is 0.  */
	cmpdi	 cr0,r5,0
	beq	 cr0,L(ret0)
	andi.   r7,r3,4095
	andi.   r8,r4,4095
	cmpldi  cr0,r7,4096-16
	cmpldi  cr1,r8,4096-16
	bgt     cr0,L(crosses)
	bgt     cr1,L(crosses)
	COMPARE_16(v4,v5,0)
	addi	r3,r3,16
	addi	r4,r4,16

L(crosses):
	andi.	 r7,r3,15
	subfic	 r7,r7,16	/* r7(nalign1) = 16 - (str1 & 15).  */
	andi.	 r9,r4,15
	subfic	 r8,r9,16	/* r8(nalign2) = 16 - (str2 & 15).  */
	cmpld	 cr7,r7,r8
	beq	 cr7,L(same_aligned)
	blt	 cr7,L(nalign1_min)

	/* nalign2 is minimum and s2 pointer is aligned.  */
	CHECK_N_BYTES(r3,r4,r8)
	/* Are we on the 64B hunk which crosses a page?  */
	andi.   r10,r3,63       /* Determine offset into 64B hunk.  */
	andi.   r8,r3,15        /* The offset into the 16B hunk.  */
	neg     r7,r3
	andi.   r9,r7,15        /* Number of bytes after a 16B cross.  */
	rlwinm. r7,r7,26,0x3F   /* ((r4-4096))>>6&63.  */
	beq     L(compare_64_pagecross)
	mtctr   r7
	b       L(compare_64B_unaligned)

	/* nalign1 is minimum and s1 pointer is aligned.  */
L(nalign1_min):
	CHECK_N_BYTES(r3,r4,r7)
	/* Are we on the 64B hunk which crosses a page?  */
	andi.   r10,r4,63       /* Determine offset into 64B hunk.  */
	andi.   r8,r4,15        /* The offset into the 16B hunk.  */
	neg     r7,r4
	andi.   r9,r7,15        /* Number of bytes after a 16B cross.  */
	rlwinm. r7,r7,26,0x3F   /* ((r4-4096))>>6&63.  */
	beq     L(compare_64_pagecross)
	mtctr   r7

	.p2align 5
L(compare_64B_unaligned):
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	COMPARE_16(v4,v5,32)
	COMPARE_16(v4,v5,48)
	addi    r3,r3,64
	addi    r4,r4,64
	bdnz    L(compare_64B_unaligned)

	/* Cross the page boundary of s2, carefully. Only for first
	iteration we have to get the count of 64B blocks to be checked.
	From second iteration and beyond, loop counter is always 63.  */
L(compare_64_pagecross):
	li      r11, 63
	mtctr   r11
	cmpldi  r10,16
	ble     L(cross_4)
	cmpldi  r10,32
	ble     L(cross_3)
	cmpldi  r10,48
	ble     L(cross_2)
L(cross_1):
	CHECK_N_BYTES(r3,r4,r9)
	CHECK_N_BYTES(r3,r4,r8)
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	COMPARE_16(v4,v5,32)
	addi    r3,r3,48
	addi    r4,r4,48
	b       L(compare_64B_unaligned)
L(cross_2):
	COMPARE_16(v4,v5,0)
	addi    r3,r3,16
	addi    r4,r4,16
	CHECK_N_BYTES(r3,r4,r9)
	CHECK_N_BYTES(r3,r4,r8)
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	addi    r3,r3,32
	addi    r4,r4,32
	b       L(compare_64B_unaligned)
L(cross_3):
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	addi    r3,r3,32
	addi    r4,r4,32
	CHECK_N_BYTES(r3,r4,r9)
	CHECK_N_BYTES(r3,r4,r8)
	COMPARE_16(v4,v5,0)
	addi    r3,r3,16
	addi    r4,r4,16
	b       L(compare_64B_unaligned)
L(cross_4):
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	COMPARE_16(v4,v5,32)
	addi    r3,r3,48
	addi    r4,r4,48
	CHECK_N_BYTES(r3,r4,r9)
	CHECK_N_BYTES(r3,r4,r8)
	b       L(compare_64B_unaligned)

L(same_aligned):
	CHECK_N_BYTES(r3,r4,r7)
	/* Align s1 to 32B and adjust s2 address.
	   Use lxvp only if both s1 and s2 are 32B aligned.  */
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	COMPARE_16(v4,v5,32)
	COMPARE_16(v4,v5,48)
	addi	r3,r3,64
	addi	r4,r4,64
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	addi	r5,r5,32

	clrldi  r6,r3,59
	subfic	r7,r6,32
	add	r3,r3,r7
	add	r4,r4,r7
	subf	r5,r7,r5
	andi.	r7,r4,0x1F
	beq	cr0,L(32B_aligned_loop)

	.p2align 5
L(16B_aligned_loop):
	COMPARE_16(v4,v5,0)
	COMPARE_16(v4,v5,16)
	COMPARE_16(v4,v5,32)
	COMPARE_16(v4,v5,48)
	addi	r3,r3,64
	addi	r4,r4,64
	b	L(16B_aligned_loop)

	/* Calculate and return the difference.  */
L(different):
	TAIL_FIRST_16B(v4,v5)

	.p2align 5
L(32B_aligned_loop):
	COMPARE_32(v14,v16,0,tail1,tail2)
	COMPARE_32(v18,v20,32,tail3,tail4)
	COMPARE_32(v22,v24,64,tail5,tail6)
	COMPARE_32(v26,v28,96,tail7,tail8)
	addi	r3,r3,128
	addi	r4,r4,128
	b	L(32B_aligned_loop)

L(tail1): TAIL_FIRST_16B(v15,v17)
L(tail2): TAIL_SECOND_16B(v14,v16)
L(tail3): TAIL_FIRST_16B(v19,v21)
L(tail4): TAIL_SECOND_16B(v18,v20)
L(tail5): TAIL_FIRST_16B(v23,v25)
L(tail6): TAIL_SECOND_16B(v22,v24)
L(tail7): TAIL_FIRST_16B(v27,v29)
L(tail8): TAIL_SECOND_16B(v26,v28)

	.p2align 5
L(ret0):
	li	r3,0
	blr

END(STRNCMP)
libc_hidden_builtin_def(strncmp)
