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package common
import "encoding/binary"
// Constant time select.
// if pick == 1 (out = in1)
// if pick == 0 (out = in2)
// else out is undefined.
func Cpick(pick int, out, in1, in2 []byte) {
var which = byte((int8(pick << 7)) >> 7)
for i := range out {
out[i] = (in1[i] & which) | (in2[i] & ^which)
}
}
// Read 2*bytelen(p) bytes into the given ExtensionFieldElement.
//
// It is an error to call this function if the input byte slice is less than 2*bytelen(p) bytes long.
func BytesToFp2(fp2 *Fp2, input []byte, bytelen int) {
if len(input) < 2*bytelen {
panic("input byte slice too short")
}
numW64 := (bytelen*8 + 63) / 64
a := make([]byte, 8*numW64)
b := make([]byte, 8*numW64)
copy(a[:bytelen], input[:bytelen])
copy(b[:bytelen], input[bytelen:])
for i := 0; i < numW64; i++ {
fp2.A[i] = binary.LittleEndian.Uint64(a[i*8 : (i+1)*8])
fp2.B[i] = binary.LittleEndian.Uint64(b[i*8 : (i+1)*8])
}
}
// Convert the input to wire format.
//
// The output byte slice must be at least 2*bytelen(p) bytes long.
func Fp2ToBytes(output []byte, fp2 *Fp2, bytelen int) {
if len(output) < 2*bytelen {
panic("output byte slice too short")
}
numW64 := (bytelen*8 + 63) / 64
a := make([]byte, 8*numW64)
b := make([]byte, 8*numW64)
for i := 0; i < numW64; i++ {
binary.LittleEndian.PutUint64(a[i*8:(i+1)*8], fp2.A[i])
binary.LittleEndian.PutUint64(b[i*8:(i+1)*8], fp2.B[i])
}
copy(output[:bytelen], a[:bytelen])
copy(output[bytelen:], b[:bytelen])
}
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