add test case

std/comparison/comparison.go

@@ -5,8 +5,8 @@ import (
 	"math/big"
 )
 
-// LogCeil returns the bit count of n
-func LogCeil(n int) int {
+// BitCount returns the number of bits of n
+func BitCount(n int) int {
 	m := 0
 	for ; n > 0; n >>= 1 {
 		m++
@@ -25,32 +25,33 @@ func BoolNeg(api frontend.API, a frontend.Variable) frontend.Variable {
 	return api.Sub(1, a)
 }
 
+// IsEqual returns 1 if a = b, otherwise return 0.
 func IsEqual(api frontend.API, a frontend.Variable, b frontend.Variable) frontend.Variable {
 	return api.IsZero(api.Sub(a, b))
 }
 
-// IsLess returns 1 if a < b
-// a and b must satisfy less than maxBits bits
+// IsLess returns 1 if a < b, otherwise return 0.
+// a and b must satisfy no more than maxBits bits
 func IsLess(api frontend.API, maxBits int, a frontend.Variable, b frontend.Variable) frontend.Variable {
 	negB := api.Neg(b)
 	bi1 := api.ToBinary(api.Add(a, OneLsh(uint(maxBits)), negB), maxBits+1)
 	return api.Sub(frontend.Variable(1), bi1[maxBits])
 }
 
-// IsGreater returns 1 if a > b
-// a and b must satisfy less than maxBits bits
+// IsGreater returns 1 if a > b, otherwise return 0.
+// a and b must satisfy no more than maxBits bits
 func IsGreater(api frontend.API, maxBits int, a frontend.Variable, b frontend.Variable) frontend.Variable {
 	return IsLess(api, maxBits, b, a)
 }
 
-// IsLessOrEqual returns 1 if a <= b
-// a and b must satisfy less than maxBits bits
+// IsLessOrEqual returns 1 if a <= b, otherwise return 0
+// a and b must satisfy no more than maxBits bits
 func IsLessOrEqual(api frontend.API, maxBits int, a frontend.Variable, b frontend.Variable) frontend.Variable {
 	return BoolNeg(api, IsGreater(api, maxBits, a, b))
 }
 
-// IsGreaterOrEqual returns 1 if a >= b
-// a and b must satisfy less than maxBits bits
+// IsGreaterOrEqual returns 1 if a >= b, otherwise return 0
+// a and b must satisfy no more than maxBits bits
 func IsGreaterOrEqual(api frontend.API, maxBits int, a frontend.Variable, b frontend.Variable) frontend.Variable {
 	return BoolNeg(api, IsLess(api, maxBits, a, b))
 }

std/comparison/comparison_test.go

@@ -0,0 +1,50 @@
+package comparison
+
+import (
+	"github.com/consensys/gnark-crypto/ecc"
+	"github.com/consensys/gnark/backend"
+	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/test"
+	"testing"
+)
+
+type comparisonCircuit struct {
+	In [4]frontend.Variable
+}
+
+func (c *comparisonCircuit) Define(api frontend.API) error {
+
+	api.AssertIsEqual(IsEqual(api, c.In[0], c.In[1]), 1)
+	api.AssertIsEqual(IsEqual(api, c.In[1], c.In[2]), 0)
+
+	for i := 0; i < len(c.In)-1; i++ {
+		api.AssertIsEqual(IsLessOrEqual(api, 8, c.In[i], c.In[i+1]), 1)
+		api.AssertIsEqual(IsGreater(api, 8, c.In[i], c.In[i+1]), 0)
+
+		api.AssertIsEqual(IsGreaterOrEqual(api, 8, c.In[i+1], c.In[i]), 1)
+		api.AssertIsEqual(IsLess(api, 8, c.In[i+1], c.In[i]), 0)
+	}
+
+	for i := 1; i < len(c.In)-1; i++ {
+		api.AssertIsEqual(IsLess(api, 8, c.In[i], c.In[i+1]), 1)
+		api.AssertIsEqual(IsGreater(api, 8, c.In[i+1], c.In[i]), 1)
+	}
+
+	return nil
+}
+
+func TestComparison(t *testing.T) {
+
+	witness := comparisonCircuit{}
+
+	witness.In[0] = 10
+	witness.In[1] = 10
+	witness.In[2] = 67
+	witness.In[3] = 255
+
+	assert := test.NewAssert(t)
+	assert.ProverSucceeded(&comparisonCircuit{}, &witness,
+		test.WithCurves(ecc.BN254),
+		test.WithBackends(backend.GROTH16, backend.PLONK),
+		test.NoFuzzing())
+}

std/hash/sha2/sha2.go

@@ -86,7 +86,7 @@ func (d *digest) FixedLengthSum(length frontend.Variable) []uints.U8 {
 	data := make([]uints.U8, len(d.in))
 	copy(data, d.in)
 
-	maxBits := comparison.LogCeil(len(data)+64*2) + 1
+	maxBits := comparison.BitCount(len(data)+64*2) + 1
 
 	for i := 0; i < 64*2; i++ {
 		data = append(data, uints.NewU8(0))