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bls12381.go
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bls12381.go
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package bls12381
import (
"math/bits"
"github.com/coinbase/kryptology/pkg/core/curves/native"
)
var fqModulusBytes = [native.FieldBytes]byte{0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x5b, 0xfe, 0xff, 0x02, 0xa4, 0xbd, 0x53, 0x05, 0xd8, 0xa1, 0x09, 0x08, 0xd8, 0x39, 0x33, 0x48, 0x7d, 0x9d, 0x29, 0x53, 0xa7, 0xed, 0x73}
const (
// The BLS parameter x for BLS12-381 is -0xd201000000010000
paramX = uint64(0xd201000000010000)
Limbs = 6
FieldBytes = 48
WideFieldBytes = 96
DoubleWideFieldBytes = 192
)
// mac Multiply and Accumulate - compute a + (b * c) + d, return the result and new carry
func mac(a, b, c, d uint64) (uint64, uint64) {
hi, lo := bits.Mul64(b, c)
carry2, carry := bits.Add64(a, d, 0)
hi, _ = bits.Add64(hi, 0, carry)
lo, carry = bits.Add64(lo, carry2, 0)
hi, _ = bits.Add64(hi, 0, carry)
return lo, hi
}
// adc Add w/Carry
func adc(x, y, carry uint64) (uint64, uint64) {
sum := x + y + carry
// The sum will overflow if both top bits are set (x & y) or if one of them
// is (x | y), and a carry from the lower place happened. If such a carry
// happens, the top bit will be 1 + 0 + 1 = 0 (&^ sum).
carryOut := ((x & y) | ((x | y) &^ sum)) >> 63
carryOut |= ((x & carry) | ((x | carry) &^ sum)) >> 63
carryOut |= ((y & carry) | ((y | carry) &^ sum)) >> 63
return sum, carryOut
}
// sbb Subtract with borrow
func sbb(x, y, borrow uint64) (uint64, uint64) {
diff := x - (y + borrow)
borrowOut := ((^x & y) | (^(x ^ y) & diff)) >> 63
return diff, borrowOut
}