feat(u128): saturating add and sub

LimeChain · Sep 27, 2023 · 9fe57ae · 9fe57ae
1 parent 8abeec4
commit 9fe57ae
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Showing 3 changed files with 60 additions and 20 deletions.
diff --git a/math.go b/math.go
@@ -102,6 +102,16 @@ func SaturatingAddU64(a, b U64) U64 {
 	return U64(sum)
 }
 
+func SaturatingAddU128(a, b U128) U128 {
+	sumLow, carry := bits.Add64(uint64(a[0]), uint64(b[0]), 0)
+	sumHigh, overflow := bits.Add64(uint64(a[1]), uint64(b[1]), carry)
+	// check for overflow
+	if overflow == 1 || (carry == 1 && sumHigh <= uint64(a[1]) && sumHigh <= uint64(b[1])) {
+		return MaxU128()
+	}
+	return U128{U64(sumLow), U64(sumHigh)}
+}
+
 func SaturatingSubU64(a, b U64) U64 {
 	diff, borrow := bits.Sub64(uint64(a), uint64(b), 0)
 	if borrow != 0 {
@@ -110,6 +120,16 @@ func SaturatingSubU64(a, b U64) U64 {
 	return U64(diff)
 }
 
+func SaturatingSubU128(a, b U128) U128 {
+	low, borrow := bits.Sub64(uint64(a[0]), uint64(b[0]), 0)
+	high, _ := bits.Sub64(uint64(a[1]), uint64(b[1]), borrow)
+	// check for underflow
+	if borrow == 1 || high > uint64(a[1]) {
+		return U128{0, 0}
+	}
+	return U128{U64(low), U64(high)}
+}
+
 func SaturatingMulU64(a, b U64) U64 {
 	if a == 0 || b == 0 {
 		return U64(0)

diff --git a/math_test.go b/math_test.go
@@ -173,6 +173,26 @@ func Test_SaturatingAddU64(t *testing.T) {
 	}
 }
 
+func Test_SaturatingAddU128(t *testing.T) {
+	testExamples := []struct {
+		label  string
+		a      U128
+		b      U128
+		expect U128
+	}{
+		{"2 + 1", NewU128(2), NewU128(1), NewU128(3)},
+		{"MaxU128+1", MaxU128(), NewU128(1), MaxU128()},
+		{"MaxU128+MaxU128", MaxU128(), MaxU128(), MaxU128()},
+	}
+
+	for _, testExample := range testExamples {
+		t.Run(testExample.label, func(t *testing.T) {
+			result := SaturatingAddU128(testExample.a, testExample.b)
+			assert.Equal(t, testExample.expect, result)
+		})
+	}
+}
+
 func Test_SaturatingSubU64(t *testing.T) {
 	testExamples := []struct {
 		label  string
@@ -192,6 +212,26 @@ func Test_SaturatingSubU64(t *testing.T) {
 	}
 }
 
+func Test_SaturatingSubU128(t *testing.T) {
+	testExamples := []struct {
+		label  string
+		a      U128
+		b      U128
+		expect U128
+	}{
+		{"2-1", NewU128(2), NewU128(1), NewU128(1)},
+		{"0-1", NewU128(0), NewU128(1), NewU128(0)},
+		{"0-MaxU128", NewU128(0), MaxU128(), NewU128(0)},
+	}
+
+	for _, testExample := range testExamples {
+		t.Run(testExample.label, func(t *testing.T) {
+			result := SaturatingSubU128(testExample.a, testExample.b)
+			assert.Equal(t, testExample.expect, result)
+		})
+	}
+}
+
 func Test_SaturatingMul(t *testing.T) {
 	testExamples := []struct {
 		label  string

diff --git a/u128.go b/u128.go
@@ -101,26 +101,6 @@ func (n U128) Gte(other U128) bool {
 	return n.ToBigInt().Cmp(other.ToBigInt()) >= 0
 }
 
-//func (n U128) SaturatingAdd(other U128) U128 {
-//	sumLow, carry := bits.Add64(uint64(n[0]), uint64(other[0]), 0)
-//	sumHigh, overflow := bits.Add64(uint64(n[1]), uint64(other[1]), carry)
-//	// check for overflow
-//	if overflow == 1 || (carry == 1 && sumHigh <= uint64(n[1]) && sumHigh <= uint64(other[1])) {
-//		return MaxU128()
-//	}
-//	return U128{U64(sumLow), U64(sumHigh)}
-//}
-//
-//func (n U128) SaturatingSub(other U128) U128 {
-//	low, borrow := bits.Sub64(uint64(n[0]), uint64(other[0]), 0)
-//	high, _ := bits.Sub64(uint64(n[1]), uint64(other[1]), borrow)
-//	// check for underflow
-//	if borrow == 1 || high > uint64(n[1]) {
-//		return U128{0, 0}
-//	}
-//	return U128{U64(low), U64(high)}
-//}
-//
 //func (n U128) SaturatingMul(other U128) U128 {
 //	result := new(big.Int).Mul(n.ToBigInt(), other.ToBigInt())
 //	// check for overflow