Eliminate bounds checks in the loop.

emmansun · Jun 21, 2023 · 36a3768 · 36a3768
1 parent 92957b5
commit 36a3768
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Showing 3 changed files with 9 additions and 9 deletions.
diff --git a/bn256/curve.go b/bn256/curve.go
@@ -270,8 +270,8 @@ func (table *curvePointTable) Select(p *curvePoint, n uint8) {
 		panic("sm9: internal error: curvePointTable called with out-of-bounds value")
 	}
 	p.SetInfinity()
-	for i := uint8(1); i < 16; i++ {
-		cond := subtle.ConstantTimeByteEq(i, n)
-		p.Select(table[i-1], p, cond)
+	for i, f := range table {
+		cond := subtle.ConstantTimeByteEq(uint8(i+1), n)
+		p.Select(f, p, cond)
 	}
 }
diff --git a/bn256/gt.go b/bn256/gt.go
@@ -216,9 +216,9 @@ func (table *GTFieldTable) Select(p *GT, n uint8) {
 		panic("sm9: internal error: GTFieldTable called with out-of-bounds value")
 	}
 	p.p.SetOne()
-	for i := uint8(1); i < 16; i++ {
-		cond := subtle.ConstantTimeByteEq(i, n)
-		p.p.Select(table[i-1].p, p.p, cond)
+	for i, f := range table {
+		cond := subtle.ConstantTimeByteEq(uint8(i+1), n)
+		p.p.Select(f.p, p.p, cond)
 	}
 }
 

diff --git a/bn256/twist.go b/bn256/twist.go
@@ -262,9 +262,9 @@ func (table *twistPointTable) Select(p *twistPoint, n uint8) {
 		panic("sm9: internal error: twistPointTable called with out-of-bounds value")
 	}
 	p.SetInfinity()
-	for i := uint8(1); i < 16; i++ {
-		cond := subtle.ConstantTimeByteEq(i, n)
-		p.Select(table[i-1], p, cond)
+	for i, f := range table {
+		cond := subtle.ConstantTimeByteEq(uint8(i+1), n)
+		p.Select(f, p, cond)
 	}
 }