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internal/bytealg: optimize index function for ppc64le/power9

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Optimized index2to16 loop by unrolling the loop by 4.
Multiple benchmark tests show performance improvement on
POWER9. Similar improvements are seen on POWER10. Added
tests to ensure changes work fine.

name            old time/op   new time/op    delta
Index/10         18.3ns ± 0%    19.7ns ±25%     ~
Index/32         75.3ns ± 0%    69.2ns ± 0%   -8.22%
Index/4K         5.53µs ± 0%    3.69µs ± 0%  -33.20%
Index/4M         5.64ms ± 0%    3.75ms ± 0%  -33.55%
Index/64M        92.9ms ± 0%    61.6ms ± 0%  -33.69%
IndexHard2       1.41ms ± 0%    0.93ms ± 0%  -33.75%
CountHard2       1.41ms ± 0%    0.93ms ± 0%  -33.75%

Change-Id: If9331df6a141a4716724b8cb648d2b91bdf17e5f
Reviewed-on: https://go-review.googlesource.com/c/go/+/377016
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Archana Ravindar <aravind5@in.ibm.com>
This commit is contained in:
Archana R 2022-01-10 02:15:25 -06:00 • committed by Lynn Boger
parent c386269ed8
commit 7ca1e2aa56
2 changed files with 149 additions and 79 deletions
Download patch file Download diff file Expand all files Collapse all files

30
src/bytes/bytes_test.go
View file

@ -140,6 +140,36 @@ var indexTests = []BinOpTest{
{"abc", "c", 2},
{"abc", "x", -1},
{"barfoobarfooyyyzzzyyyzzzyyyzzzyyyxxxzzzyyy", "x", 33},
{"fofofofooofoboo", "oo", 7},
{"fofofofofofoboo", "ob", 11},
{"fofofofofofoboo", "boo", 12},
{"fofofofofofoboo", "oboo", 11},
{"fofofofofoooboo", "fooo", 8},
{"fofofofofofoboo", "foboo", 10},
{"fofofofofofoboo", "fofob", 8},
{"fofofofofofofoffofoobarfoo", "foffof", 12},
{"fofofofofoofofoffofoobarfoo", "foffof", 13},
{"fofofofofofofoffofoobarfoo", "foffofo", 12},
{"fofofofofoofofoffofoobarfoo", "foffofo", 13},
{"fofofofofoofofoffofoobarfoo", "foffofoo", 13},
{"fofofofofofofoffofoobarfoo", "foffofoo", 12},
{"fofofofofoofofoffofoobarfoo", "foffofoob", 13},
{"fofofofofofofoffofoobarfoo", "foffofoob", 12},
{"fofofofofoofofoffofoobarfoo", "foffofooba", 13},
{"fofofofofofofoffofoobarfoo", "foffofooba", 12},
{"fofofofofoofofoffofoobarfoo", "foffofoobar", 13},
{"fofofofofofofoffofoobarfoo", "foffofoobar", 12},
{"fofofofofoofofoffofoobarfoo", "foffofoobarf", 13},
{"fofofofofofofoffofoobarfoo", "foffofoobarf", 12},
{"fofofofofoofofoffofoobarfoo", "foffofoobarfo", 13},
{"fofofofofofofoffofoobarfoo", "foffofoobarfo", 12},
{"fofofofofoofofoffofoobarfoo", "foffofoobarfoo", 13},
{"fofofofofofofoffofoobarfoo", "foffofoobarfoo", 12},
{"fofofofofoofofoffofoobarfoo", "ofoffofoobarfoo", 12},
{"fofofofofofofoffofoobarfoo", "ofoffofoobarfoo", 11},
{"fofofofofoofofoffofoobarfoo", "fofoffofoobarfoo", 11},
{"fofofofofofofoffofoobarfoo", "fofoffofoobarfoo", 10},
{"fofofofofoofofoffofoobarfoo", "foobars", -1},
{"foofyfoobarfoobar", "y", 4},
{"oooooooooooooooooooooo", "r", -1},
{"oxoxoxoxoxoxoxoxoxoxoxoy", "oy", 22},

198
src/internal/bytealg/index_ppc64x.s
View file

@ -17,8 +17,9 @@
// NOTE: There is a power9 implementation that
// improves performance by 10-15% on little
// endian for some of the benchmarks, but
// work is still needed for a big endian
// endian for some of the benchmarks.
// Unrolled index2to16 loop by 4 on ppc64le/power9
// Work is still needed for a big endian
// implementation on power9.
//go:build ppc64 || ppc64le
@ -46,8 +47,8 @@ DATA byteswap<>+8(SB)/8, $0x0f0e0d0c0b0a0908
GLOBL byteswap<>+0(SB), RODATA, $16
TEXT ·Index<ABIInternal>(SB),NOSPLIT|NOFRAME,$0-56
// R3 = byte array pointer
// R4 = length
// R3 = byte array pointer
// R4 = length
MOVD R6, R5 // R5 = separator pointer
MOVD R7, R6 // R6 = separator length
@ -97,16 +98,6 @@ power8:
#define LASTSTR R27
#define ONES V20
#define SWAP V21
#define V0_ VS32
#define V1_ VS33
#define V2_ VS34
#define V3_ VS35
#define V4_ VS36
#define V5_ VS37
#define V6_ VS38
#define V7_ VS39
#define V8_ VS40
#define V9_ VS41
#define SWAP_ VS53
TEXT indexbody<>(SB), NOSPLIT|NOFRAME, $0
CMP R6, R4 // Compare lengths
@ -129,7 +120,7 @@ TEXT indexbody<>(SB), NOSPLIT|NOFRAME, $0
BGE CR4, loadge16 // Load for len(sep) >= 16
SUB R6, R16, R9 // 16-len of sep
SLD $3, R9 // Set up for VSLO
MTVSRD R9, V9_ // Set up for VSLO
MTVSRD R9, V9 // Set up for VSLO
VSLDOI $8, V9, V9, V9 // Set up for VSLO
VSLO ONES, V9, SEPMASK // Mask for separator len(sep) < 16
@ -140,9 +131,9 @@ loadge16:
BGT sepcross16 // Sep crosses 16 byte boundary
RLDICR $0, R5, $59, R8 // Adjust addr to 16 byte container
VLOADSWAP(R8, R0, V0, V0_)// Load 16 bytes @R8 into V0
VLOADSWAP(R8, R0, V0, V0) // Load 16 bytes @R8 into V0
SLD $3, R9 // Set up shift count for VSLO
MTVSRD R9, V8_ // Set up shift count for VSLO
MTVSRD R9, V8 // Set up shift count for VSLO
VSLDOI $8, V8, V8, V8
VSLO V0, V8, V0 // Shift by start byte
@ -150,7 +141,7 @@ loadge16:
BR index2plus
sepcross16:
VLOADSWAP(R5, R0, V0, V0_) // Load 16 bytes @R5 into V0
VLOADSWAP(R5, R0, V0, V0) // Load 16 bytes @R5 into V0
VAND V0, SEPMASK, V0 // mask out separator
BLE CR4, index2to16
@ -179,10 +170,10 @@ index2plus:
// that value when found. Loop as
// long as len(string) > 16
index2loop2:
VLOADSWAP(R7, R19, V3, V3_) // Load 16 bytes @R7+1 into V3
VLOADSWAP(R7, R19, V3, V3) // Load 16 bytes @R7+1 into V3
index2loop:
VLOADSWAP(R7, R0, V2, V2_) // Load 16 bytes @R7 into V2
VLOADSWAP(R7, R0, V2, V2) // Load 16 bytes @R7 into V2
VCMPEQUH V1, V2, V5 // Search for sep
VCMPEQUH V1, V3, V6 // Search for sep offset by 1
VSEL V6, V5, V31, V7 // merge even and odd indices
@ -201,7 +192,7 @@ index2loop:
BLT index2loop2 // If < last, continue loop
CMP R7, LASTBYTE // Compare addr+16 against last byte
BLT index2to16 // If < 16 handle specially
VLOADSWAP(R7, R0, V3, V3_) // Load 16 bytes @R7 into V3
VLOADSWAP(R7, R0, V3, V3) // Load 16 bytes @R7 into V3
VSLDOI $1, V3, V10, V3 // Shift left by 1 byte
BR index2loop
@ -234,11 +225,11 @@ index3plus:
index3loop2:
MOVD $2, R21 // Set up index for 2
VSPLTISB $0, V10 // Clear V10
VLOADSWAP(R7, R21, V3, V3_)// Load 16 bytes @R7+2 into V3
VLOADSWAP(R7, R21, V3, V3)// Load 16 bytes @R7+2 into V3
VSLDOI $14, V3, V10, V3 // Left justify next 2 bytes
index3loop:
VLOADSWAP(R7, R0, V2, V2_) // Load with correct order
VLOADSWAP(R7, R0, V2, V2) // Load with correct order
VSLDOI $1, V2, V3, V4 // string[1:17]
VSLDOI $2, V2, V3, V9 // string[2:18]
VCMPEQUH V1, V2, V5 // compare hw even indices
@ -294,12 +285,12 @@ index4plus:
VSPLTW $0, V0, V1 // Splat 1st word of separator
index4loop:
VLOADSWAP(R7, R0, V2, V2_) // Load 16 bytes @R7 into V2
VLOADSWAP(R7, R0, V2, V2) // Load 16 bytes @R7 into V2
next4:
VSPLTISB $0, V10 // Clear
MOVD $3, R9 // Number of bytes beyond 16
VLOADSWAP(R7, R9, V3, V3_) // Load 16 bytes @R7+3 into V3
VLOADSWAP(R7, R9, V3, V3) // Load 16 bytes @R7+3 into V3
VSLDOI $13, V3, V10, V3 // Shift left last 3 bytes
VSLDOI $1, V2, V3, V4 // V4=(V2:V3)<<1
VSLDOI $2, V2, V3, V9 // V9=(V2:V3)<<2
@ -344,7 +335,7 @@ index2to16:
// At least 16 bytes of string left
// Mask the number of bytes in sep
index2to16loop:
VLOADSWAP(R7, R0, V1, V1_) // Load 16 bytes @R7 into V1
VLOADSWAP(R7, R0, V1, V1) // Load 16 bytes @R7 into V1
compare:
VAND V1, SEPMASK, V2 // Mask out sep size
@ -366,14 +357,14 @@ index2to16tail:
ADD R10, R9, R11 // offset + len
CMP R11, $16 // >= 16?
BLE short // Does not cross 16 bytes
VLOADSWAP(R7, R0, V1, V1_)// Load 16 bytes @R7 into V1
VLOADSWAP(R7, R0, V1, V1) // Load 16 bytes @R7 into V1
BR index2to16next // Continue on
short:
RLDICR $0, R7, $59, R9 // Adjust addr to 16 byte container
VLOADSWAP(R9, R0, V1, V1_)// Load 16 bytes @R9 into V1
VLOADSWAP(R9, R0, V1, V1)// Load 16 bytes @R9 into V1
SLD $3, R10 // Set up shift
MTVSRD R10, V8_ // Set up shift
MTVSRD R10, V8 // Set up shift
VSLDOI $8, V8, V8, V8
VSLO V1, V8, V1 // Shift by start byte
VSPLTISB $0, V25 // Clear for later use
@ -393,17 +384,17 @@ index17plus:
BGT index33plus
SUB $16, R6, R9 // Extra > 16
SLD $56, R9, R10 // Shift to use in VSLO
MTVSRD R10, V9_ // Set up for VSLO
VLOADSWAP(R5, R9, V1, V1_)// Load 16 bytes @R5+R9 into V1
MTVSRD R10, V9 // Set up for VSLO
VLOADSWAP(R5, R9, V1, V1)// Load 16 bytes @R5+R9 into V1
VSLO V1, V9, V1 // Shift left
VSPLTISB $0xff, V7 // Splat 1s
VSPLTISB $0, V27 // Splat 0
index17to32loop:
VLOADSWAP(R7, R0, V2, V2_) // Load 16 bytes @R7 into V2
VLOADSWAP(R7, R0, V2, V2) // Load 16 bytes @R7 into V2
next17:
VLOADSWAP(R7, R9, V3, V3_) // Load 16 bytes @R7+R9 into V3
VLOADSWAP(R7, R9, V3, V3) // Load 16 bytes @R7+R9 into V3
VSLO V3, V9, V3 // Shift left
VCMPEQUB V0, V2, V4 // Compare first 16 bytes
VCMPEQUB V1, V3, V5 // Compare extra over 16 bytes
@ -454,7 +445,7 @@ TEXT indexbodyp9<>(SB), NOSPLIT|NOFRAME, $0
BGE CR4, loadge16 // Load for len(sep) >= 16
SUB R6, R16, R9 // 16-len of sep
SLD $3, R9 // Set up for VSLO
MTVSRD R9, V9_ // Set up for VSLO
MTVSRD R9, V9 // Set up for VSLO
VSLDOI $8, V9, V9, V9 // Set up for VSLO
VSLO ONES, V9, SEPMASK // Mask for separator len(sep) < 16
@ -465,9 +456,9 @@ loadge16:
BGT sepcross16 // Sep crosses 16 byte boundary
RLDICR $0, R5, $59, R8 // Adjust addr to 16 byte container
LXVB16X (R8)(R0), V0_ // Load 16 bytes @R8 into V0
LXVB16X (R8)(R0), V0 // Load 16 bytes @R8 into V0
SLD $3, R9 // Set up shift count for VSLO
MTVSRD R9, V8_ // Set up shift count for VSLO
MTVSRD R9, V8 // Set up shift count for VSLO
VSLDOI $8, V8, V8, V8
VSLO V0, V8, V0 // Shift by start byte
@ -475,7 +466,7 @@ loadge16:
BR index2plus
sepcross16:
LXVB16X (R5)(R0), V0_ // Load 16 bytes @R5 into V0
LXVB16X (R5)(R0), V0 // Load 16 bytes @R5 into V0
VAND V0, SEPMASK, V0 // mask out separator
BLE CR4, index2to16
@ -504,10 +495,10 @@ index2plus:
// that value when found. Loop as
// long as len(string) > 16
index2loop2:
LXVB16X (R7)(R19), V3_ // Load 16 bytes @R7+1 into V3
LXVB16X (R7)(R19), V3 // Load 16 bytes @R7+1 into V3
index2loop:
LXVB16X (R7)(R0), V2_ // Load 16 bytes @R7 into V2
LXVB16X (R7)(R0), V2 // Load 16 bytes @R7 into V2
VCMPEQUH V1, V2, V5 // Search for sep
VCMPEQUH V1, V3, V6 // Search for sep offset by 1
VSEL V6, V5, V31, V7 // merge even and odd indices
@ -526,7 +517,7 @@ index2loop:
BLT index2loop2 // If < last, continue loop
CMP R7, LASTBYTE // Compare addr+16 against last byte
BLT index2to16 // If < 16 handle specially
LXVB16X (R7)(R0), V3_ // Load 16 bytes @R7 into V3
LXVB16X (R7)(R0), V3 // Load 16 bytes @R7 into V3
VSLDOI $1, V3, V10, V3 // Shift left by 1 byte
BR index2loop
@ -559,11 +550,11 @@ index3plus:
index3loop2:
MOVD $2, R21 // Set up index for 2
VSPLTISB $0, V10 // Clear V10
LXVB16X (R7)(R21), V3_ // Load 16 bytes @R7+2 into V3
LXVB16X (R7)(R21), V3 // Load 16 bytes @R7+2 into V3
VSLDOI $14, V3, V10, V3 // Left justify next 2 bytes
index3loop:
LXVB16X (R7)(R0), V2_ // Load 16 bytes @R7
LXVB16X (R7)(R0), V2 // Load 16 bytes @R7
VSLDOI $1, V2, V3, V4 // string[1:17]
VSLDOI $2, V2, V3, V9 // string[2:18]
VCMPEQUH V1, V2, V5 // compare hw even indices
@ -604,7 +595,6 @@ index4plus:
ADD $20, R7, R9 // Check string size to load
CMP R9, LASTBYTE // Verify string length
BGE index2to16 // If not large enough, process remaining
MOVD $2, R15 // Set up index
// Set up masks for use with VSEL
MOVD $0xff, R21 // Set up mask 0xff000000ff000000...
@ -619,12 +609,12 @@ index4plus:
VSPLTW $0, V0, V1 // Splat 1st word of separator
index4loop:
LXVB16X (R7)(R0), V2_ // Load 16 bytes @R7 into V2
LXVB16X (R7)(R0), V2 // Load 16 bytes @R7 into V2
next4:
VSPLTISB $0, V10 // Clear
MOVD $3, R9 // Number of bytes beyond 16
LXVB16X (R7)(R9), V3_ // Load 16 bytes @R7 into V2
LXVB16X (R7)(R9), V3 // Load 16 bytes @R7 into V2
VSLDOI $13, V3, V10, V3 // Shift left last 3 bytes
VSLDOI $1, V2, V3, V4 // V4=(V2:V3)<<1
VSLDOI $2, V2, V3, V9 // V9=(V2:V3)<<2
@ -662,46 +652,91 @@ index2to16:
CMP R7, LASTSTR // Compare last start byte
BGT notfound // last takes len(sep) into account
ADD $16, R7, R9 // Check for last byte of string
ADD $19, R7, R9 // To check 4 indices per iteration, need at least 16+3 bytes
CMP R9, LASTBYTE
BGT index2to16tail
// At least 16 bytes of string left
// Mask the number of bytes in sep
index2to16loop:
LXVB16X (R7)(R0), V1_ // Load 16 bytes @R7 into V1
VSPLTISB $0, V10 // Clear
MOVD $3, R17 // Number of bytes beyond 16
compare:
VAND V1, SEPMASK, V2 // Mask out sep size
VCMPEQUBCC V0, V2, V3 // Compare masked string
BLT CR6, found // All equal
ADD $1, R7 // Update ptr to next byte
index2to16loop:
LXVB16X (R7)(R0), V1 // Load next 16 bytes of string into V1 from R7
LXVB16X (R7)(R17), V5 // Load next 16 bytes of string into V5 from R7+3
VSLDOI $13, V5, V10, V2 // Shift left last 3 bytes
VSLDOI $1, V1, V2, V3 // V3=(V1:V2)<<1
VSLDOI $2, V1, V2, V4 // V4=(V1:V2)<<2
VAND V1, SEPMASK, V8 // Mask out sep size 0th index
VAND V3, SEPMASK, V9 // Mask out sep size 1st index
VAND V4, SEPMASK, V11 // Mask out sep size 2nd index
VAND V5, SEPMASK, V12 // Mask out sep size 3rd index
VCMPEQUBCC V0, V8, V8 // compare masked string
BLT CR6, found // All equal while comparing 0th index
VCMPEQUBCC V0, V9, V9 // compare masked string
BLT CR6, found2 // All equal while comparing 1st index
VCMPEQUBCC V0, V11, V11 // compare masked string
BLT CR6, found3 // All equal while comparing 2nd index
VCMPEQUBCC V0, V12, V12 // compare masked string
BLT CR6, found4 // All equal while comparing 3rd index
ADD $4, R7 // Update ptr to next 4 bytes
CMP R7, LASTSTR // Still less than last start byte
BGT notfound // Not found
ADD $16, R7, R9 // Verify remaining bytes
CMP R9, LASTBYTE // At least 16
BLT index2to16loop // Try again
ADD $19, R7, R9 // Verify remaining bytes
CMP R9, LASTBYTE // length of string at least 19
BLE index2to16loop // Try again, else do post processing and jump to index2to16next
// Less than 16 bytes remaining in string
// Separator >= 2
// <19 bytes left, post process the remaining string
index2to16tail:
ADD R3, R4, R9 // End of string
SUB R7, R9, R9 // Number of bytes left
ANDCC $15, R7, R10 // 16 byte offset
ADD R10, R9, R11 // offset + len
CMP R11, $16 // >= 16?
BLE short // Does not cross 16 bytes
LXVB16X (R7)(R0), V1_ // Load 16 bytes @R7 into V1
BR index2to16next // Continue on
ADD R3, R4, R9 // End of string
SUB R7, R9, R9 // Number of bytes left
ANDCC $15, R7, R10 // 16 byte offset
ADD R10, R9, R11 // offset + len
CMP R11, $16 // >= 16?
BLE short // Does not cross 16 bytes
LXVB16X (R7)(R0), V1 // Load 16 bytes @R7 into V1
CMP R9, $16 // Post-processing of unrolled loop
BLE index2to16next // continue to index2to16next if <= 16 bytes
SUB R16, R9, R10 // R9 should be 18 or 17 hence R10 is 1 or 2
LXVB16X (R7)(R10), V9
CMP R10, $1 // string length is 17, compare 1 more byte
BNE extra2 // string length is 18, compare 2 more bytes
VSLDOI $15, V9, V10, V25
VAND V1, SEPMASK, V2 // Just compare size of sep
VCMPEQUBCC V0, V2, V3 // Compare sep and partial string
BLT CR6, found // Found
ADD $1, R7 // Not found, try next partial string
CMP R7, LASTSTR // Check for end of string
BGT notfound // If at end, then not found
VSLDOI $1, V1, V25, V1 // Shift string left by 1 byte
BR index2to16next // go to remainder loop
extra2:
VSLDOI $14, V9, V10, V25
VAND V1, SEPMASK, V2 // Just compare size of sep
VCMPEQUBCC V0, V2, V3 // Compare sep and partial string
BLT CR6, found // Found
ADD $1, R7 // Not found, try next partial string
CMP R7, LASTSTR // Check for end of string
BGT notfound // If at end, then not found
VSLDOI $1, V1, V25, V1 // Shift string left by 1 byte
VAND V1, SEPMASK, V2 // Just compare size of sep
VCMPEQUBCC V0, V2, V3 // Compare sep and partial string
BLT CR6, found // Found
ADD $1, R7 // Not found, try next partial string
CMP R7, LASTSTR // Check for end of string
BGT notfound // If at end, then not found
VSLDOI $1, V1, V25, V1 // Shift string left by 1 byte
BR index2to16next // Check the remaining partial string in index2to16next
short:
RLDICR $0, R7, $59, R9 // Adjust addr to 16 byte container
LXVB16X (R9)(R0), V1_ // Load 16 bytes @R9 into V1
SLD $3, R10 // Set up shift
MTVSRD R10, V8_ // Set up shift
RLDICR $0, R7, $59, R9 // Adjust addr to 16 byte container
LXVB16X (R9)(R0), V1 // Load 16 bytes @R9 into V1
SLD $3, R10 // Set up shift
MTVSRD R10, V8 // Set up shift
VSLDOI $8, V8, V8, V8
VSLO V1, V8, V1 // Shift by start byte
VSPLTISB $0, V25 // Clear for later use
VSLO V1, V8, V1 // Shift by start byte
index2to16next:
VAND V1, SEPMASK, V2 // Just compare size of sep
@ -710,7 +745,7 @@ index2to16next:
ADD $1, R7 // Not found, try next partial string
CMP R7, LASTSTR // Check for end of string
BGT notfound // If at end, then not found
VSLDOI $1, V1, V25, V1 // Shift string left by 1 byte
VSLDOI $1, V1, V10, V1 // Shift string left by 1 byte
BR index2to16next // Check the next partial string
index17plus:
@ -718,17 +753,17 @@ index17plus:
BGT index33plus
SUB $16, R6, R9 // Extra > 16
SLD $56, R9, R10 // Shift to use in VSLO
MTVSRD R10, V9_ // Set up for VSLO
LXVB16X (R5)(R9), V1_ // Load 16 bytes @R5+R9 into V1
MTVSRD R10, V9 // Set up for VSLO
LXVB16X (R5)(R9), V1 // Load 16 bytes @R5+R9 into V1
VSLO V1, V9, V1 // Shift left
VSPLTISB $0xff, V7 // Splat 1s
VSPLTISB $0, V27 // Splat 0
index17to32loop:
LXVB16X (R7)(R0), V2_ // Load 16 bytes @R7 into V2
LXVB16X (R7)(R0), V2 // Load 16 bytes @R7 into V2
next17:
LXVB16X (R7)(R9), V3_ // Load 16 bytes @R7+R9 into V3
LXVB16X (R7)(R9), V3 // Load 16 bytes @R7+R9 into V3
VSLO V3, V9, V3 // Shift left
VCMPEQUB V0, V2, V4 // Compare first 16 bytes
VCMPEQUB V1, V3, V5 // Compare extra over 16 bytes
@ -754,8 +789,13 @@ foundR25:
SUB R3, R7 // Subtract from start of string
MOVD R7, R3 // Return byte where found
RET
found:
found4:
ADD $1, R7 // found from unrolled loop at index 3
found3:
ADD $1, R7 // found from unrolled loop at index 2
found2:
ADD $1, R7 // found from unrolled loop at index 1
found: // found at index 0
SUB R3, R7 // Return byte where found
MOVD R7, R3
RET