// Copyright 2019 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

#include "go_asm.h"

#include "textflag.h"

// condition code masks

#define EQ 8

#define NE 7

// register assignments

#define R_ZERO R0

#define R_VAL R1

#define R_TMP R2

#define R_PTR R3

#define R_LEN R4

#define R_CHAR R5

#define R_RET R6

#define R_ITER R7

#define R_CNT R8

#define R_MPTR R9

// vector register assignments

#define V_ZERO V0

#define V_CHAR V1

#define V_MASK V2

#define V_VAL V3

#define V_CNT V4

// mask for trailing bytes in vector implementation

GLOBL countbytemask<>(SB), RODATA, $16

DATA countbytemask<>+0(SB)/8, $0x0101010101010101

DATA countbytemask<>+8(SB)/8, $0x0101010101010101

// func Count(b []byte, c byte) int

TEXT ·Count(SB), NOSPLIT|NOFRAME, $0-40

LMG b+0(FP), R_PTR, R_LEN

MOVBZ c+24(FP), R_CHAR

MOVD $ret+32(FP), R_RET

BR countbytebody<>(SB)

// func CountString(s string, c byte) int

TEXT ·CountString(SB), NOSPLIT|NOFRAME, $0-32

LMG s+0(FP), R_PTR, R_LEN

MOVBZ c+16(FP), R_CHAR

MOVD $ret+24(FP), R_RET

BR countbytebody<>(SB)

// input:

// R_PTR = address of array of bytes

// R_LEN = number of bytes in array

// R_CHAR = byte value to count zero (extended to register width)

// R_RET = address of return value

TEXT countbytebody<>(SB), NOSPLIT|NOFRAME, $0-0

MOVD $internal∕cpu·S390X+const_offsetS390xHasVX(SB), R_TMP

MOVD $countbytemask<>(SB), R_MPTR

CGIJ $EQ, R_LEN, $0, ret0 // return if length is 0.

SRD $4, R_LEN, R_ITER // R_ITER is the number of 16-byte chunks

MOVBZ (R_TMP), R_TMP // load bool indicating support for vector facility

CGIJ $EQ, R_TMP, $0, novx // jump to scalar code if the vector facility is not available

// Start of vector code (have vector facility).

//

// Set R_LEN to be the length mod 16 minus 1 to use as an index for

// vector 'load with length' (VLL). It will be in the range [-1,14].

// Also replicate c across a 16-byte vector and initialize V_ZERO.

ANDW $0xf, R_LEN

VLVGB $0, R_CHAR, V_CHAR // V_CHAR = [16]byte{c, 0, ..., 0, 0}

VZERO V_ZERO // V_ZERO = [1]uint128{0}

ADDW $-1, R_LEN

VREPB $0, V_CHAR, V_CHAR // V_CHAR = [16]byte{c, c, ..., c, c}

// Jump to loop if we have more than 15 bytes to process.

CGIJ $NE, R_ITER, $0, vxchunks

// Load 1-15 bytes and corresponding mask.

// Note: only the low 32-bits of R_LEN are used for the index.

VLL R_LEN, (R_PTR), V_VAL

VLL R_LEN, (R_MPTR), V_MASK

// Compare each byte in input chunk against byte to be counted.

// Each byte element will be set to either 0 (no match) or 1 (match).

VCEQB V_CHAR, V_VAL, V_VAL // each byte will be either 0xff or 0x00

VN V_MASK, V_VAL, V_VAL // mask out most significant 7 bits

// Accumulate matched byte count in 128-bit integer value.

VSUMB V_VAL, V_ZERO, V_VAL // [16]byte{x0, x1, ..., x14, x15} → [4]uint32{x0+x1+x2+x3, ..., x12+x13+x14+x15}

VSUMQF V_VAL, V_ZERO, V_CNT // [4]uint32{x0, x1, x2, x3} → [1]uint128{x0+x1+x2+x3}

// Return rightmost (lowest) 64-bit part of accumulator.

VSTEG $1, V_CNT, (R_RET)

RET

vxchunks:

// Load 0x01 into every byte element in the 16-byte mask vector.

VREPIB $1, V_MASK // V_MASK = [16]byte{1, 1, ..., 1, 1}

VZERO V_CNT // initial uint128 count of 0

vxloop:

// Load input bytes in 16-byte chunks.

VL (R_PTR), V_VAL

// Compare each byte in input chunk against byte to be counted.

// Each byte element will be set to either 0 (no match) or 1 (match).

VCEQB V_CHAR, V_VAL, V_VAL // each byte will be either 0xff or 0x00

VN V_MASK, V_VAL, V_VAL // mask out most significant 7 bits

// Increment input string address.

MOVD $16(R_PTR), R_PTR

// Accumulate matched byte count in 128-bit integer value.

VSUMB V_VAL, V_ZERO, V_VAL // [16]byte{x0, x1, ..., x14, x15} → [4]uint32{x0+x1+x2+x3, ..., x12+x13+x14+x15}

VSUMQF V_VAL, V_ZERO, V_VAL // [4]uint32{x0, x1, x2, x3} → [1]uint128{x0+x1+x2+x3}

VAQ V_VAL, V_CNT, V_CNT // accumulate

// Repeat until all 16-byte chunks are done.

BRCTG R_ITER, vxloop

// Skip to end if there are no trailing bytes.

CIJ $EQ, R_LEN, $-1, vxret

// Load 1-15 bytes and corresponding mask.

// Note: only the low 32-bits of R_LEN are used for the index.

VLL R_LEN, (R_PTR), V_VAL

VLL R_LEN, (R_MPTR), V_MASK

// Compare each byte in input chunk against byte to be counted.

// Each byte element will be set to either 0 (no match) or 1 (match).

VCEQB V_CHAR, V_VAL, V_VAL

VN V_MASK, V_VAL, V_VAL

// Accumulate matched byte count in 128-bit integer value.

VSUMB V_VAL, V_ZERO, V_VAL // [16]byte{x0, x1, ..., x14, x15} → [4]uint32{x0+x1+x2+x3, ..., x12+x13+x14+x15}

VSUMQF V_VAL, V_ZERO, V_VAL // [4]uint32{x0, x1, x2, x3} → [1]uint128{x0+x1+x2+x3}

VAQ V_VAL, V_CNT, V_CNT // accumulate

vxret:

// Return rightmost (lowest) 64-bit part of accumulator.

VSTEG $1, V_CNT, (R_RET)

RET

novx:

// Start of non-vector code (the vector facility not available).

//

// Initialise counter and constant zero.

MOVD $0, R_CNT

MOVD $0, R_ZERO

loop:

// Read 1-byte from input and compare.

// Note: avoid putting LOCGR in critical path.

MOVBZ (R_PTR), R_VAL

MOVD $1, R_TMP

MOVD $1(R_PTR), R_PTR

CMPW R_VAL, R_CHAR

LOCGR $NE, R_ZERO, R_TMP // select 0 if no match (1 if there is a match)

ADD R_TMP, R_CNT // accumulate 64-bit result

// Repeat until all bytes have been checked.

BRCTG R_LEN, loop

ret:

MOVD R_CNT, (R_RET)

RET

ret0:

MOVD $0, (R_RET)

RET