examples: simplify FNV1A loop

mmcloughlin · Apr 7, 2022 · 740992a · 740992a
1 parent 72b8db9
commit 740992a
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Showing 3 changed files with 8 additions and 8 deletions.
diff --git a/examples/fnv1a/README.md b/examples/fnv1a/README.md
@@ -13,22 +13,22 @@ func main() {
 	TEXT("Hash64", NOSPLIT, "func(data []byte) uint64")
 	Doc("Hash64 computes the FNV-1a hash of data.")
 	ptr := Load(Param("data").Base(), GP64())
-	n := Load(Param("data").Len(), GP64())
+	endPtr := Load(Param("data").Len(), GP64())
+	ADDQ(ptr, endPtr)
 
 	h := RAX
 	MOVQ(Imm(OffsetBasis), h)
 	p := GP64()
 	MOVQ(Imm(Prime), p)
 
 	Label("loop")
-	CMPQ(n, Imm(0))
+	CMPQ(ptr, endPtr)
 	JE(LabelRef("done"))
 	b := GP64()
 	MOVBQZX(Mem{Base: ptr}, b)
 	XORQ(b, h)
 	MULQ(p)
 	INCQ(ptr)
-	DECQ(n)
 
 	JMP(LabelRef("loop"))
 	Label("done")

diff --git a/examples/fnv1a/asm.go b/examples/fnv1a/asm.go
@@ -18,22 +18,22 @@ func main() {
 	TEXT("Hash64", NOSPLIT, "func(data []byte) uint64")
 	Doc("Hash64 computes the FNV-1a hash of data.")
 	ptr := Load(Param("data").Base(), GP64())
-	n := Load(Param("data").Len(), GP64())
+	endPtr := Load(Param("data").Len(), GP64())
+	ADDQ(ptr, endPtr)
 
 	h := RAX
 	MOVQ(Imm(OffsetBasis), h)
 	p := GP64()
 	MOVQ(Imm(Prime), p)
 
 	Label("loop")
-	CMPQ(n, Imm(0))
+	CMPQ(ptr, endPtr)
 	JE(LabelRef("done"))
 	b := GP64()
 	MOVBQZX(Mem{Base: ptr}, b)
 	XORQ(b, h)
 	MULQ(p)
 	INCQ(ptr)
-	DECQ(n)
 
 	JMP(LabelRef("loop"))
 	Label("done")

diff --git a/examples/fnv1a/fnv1a.s b/examples/fnv1a/fnv1a.s
@@ -6,17 +6,17 @@
 TEXT ·Hash64(SB), NOSPLIT, $0-32
 	MOVQ data_base+0(FP), CX
 	MOVQ data_len+8(FP), BX
+	ADDQ CX, BX
 	MOVQ $0xcbf29ce484222325, AX
 	MOVQ $0x00000100000001b3, SI
 
 loop:
-	CMPQ    BX, $0x00
+	CMPQ    CX, BX
 	JE      done
 	MOVBQZX (CX), DX
 	XORQ    DX, AX
 	MULQ    SI
 	INCQ    CX
-	DECQ    BX
 	JMP     loop
 
 done: