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// +build ignore
package main
import (
. "github.com/mmcloughlin/avo/build"
. "github.com/mmcloughlin/avo/operand"
)
func init() {
ConstraintExpr("!purego")
}
func main() {
TEXT("intersect16", NOSPLIT, "func(dst, a, b []byte) int")
// Load all pointers.
dst := Load(Param("dst").Base(), GP64())
a := Load(Param("a").Base(), GP64())
b := Load(Param("b").Base(), GP64())
// Calculate the end of a/b so we know where to loop until.
aEnd := Load(Param("a").Len(), GP64())
ADDQ(a, aEnd)
bEnd := Load(Param("b").Len(), GP64())
ADDQ(b, bEnd)
ones := XMM()
VPCMPEQB(ones, ones, ones)
// Load the first item from a/b. We know that each has at least
// one item (this is enforced in the wrapper).
aItem := XMM()
bItem := XMM()
VMOVUPS(Mem{Base: a}, aItem)
VMOVUPS(Mem{Base: b}, bItem)
Label("loop")
// Compare bytes and extract two masks.
// ne = mask of bytes where a!=b
// lt = mask of bytes where a<b
ne := XMM()
lt := XMM()
VPCMPEQB(aItem, bItem, ne)
VPXOR(ne, ones, ne)
VPMINUB(aItem, bItem, lt)
VPCMPEQB(aItem, lt, lt)
VPAND(lt, ne, lt)
unequalMask := GP32()
lessMask := GP32()
VPMOVMSKB(ne, unequalMask)
VPMOVMSKB(lt, lessMask)
// Branch based on whether a==b, or a<b.
TESTL(unequalMask, unequalMask)
JZ(LabelRef("equal"))
unequalByteIndex := GP32()
BSFL(unequalMask, unequalByteIndex)
BTSL(unequalByteIndex, lessMask)
JCS(LabelRef("less"))
// If b<a, advance b.
Label("greater")
ADDQ(Imm(16), b)
CMPQ(b, bEnd)
JE(LabelRef("done"))
VMOVUPS(Mem{Base: b}, bItem)
JMP(LabelRef("loop"))
// If a<b, advance a.
Label("less")
ADDQ(Imm(16), a)
CMPQ(a, aEnd)
JE(LabelRef("done"))
VMOVUPS(Mem{Base: a}, aItem)
JMP(LabelRef("loop"))
// If a==b, copy either and advance both.
Label("equal")
VMOVUPS(aItem, Mem{Base: dst})
ADDQ(Imm(16), dst)
ADDQ(Imm(16), a)
ADDQ(Imm(16), b)
CMPQ(a, aEnd)
JE(LabelRef("done"))
CMPQ(b, bEnd)
JE(LabelRef("done"))
VMOVUPS(Mem{Base: a}, aItem)
VMOVUPS(Mem{Base: b}, bItem)
JMP(LabelRef("loop"))
// Calculate and return byte offset of the dst pointer.
Label("done")
SUBQ(Load(Param("dst").Base(), GP64()), dst)
Store(dst, ReturnIndex(0))
RET()
Generate()
}
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