Function cSwap2 [src]

Conditionally swap two pairs of field elements if c is positive

Prototype

pub fn cSwap2(a0: *Fe, b0: *Fe, a1: *Fe, b1: *Fe, c: u64) void

Parameters

a0: *Feb0: *Fea1: *Feb1: *Fec: u64

Source

  pub fn cSwap2(a0: *Fe, b0: *Fe, a1: *Fe, b1: *Fe, c: u64) void {
    const mask: u64 = 0 -% c;
    var x0 = a0.*;
    var x1 = a1.*;
    comptime var i = 0;
    inline while (i < 5) : (i += 1) {
        x0.limbs[i] ^= b0.limbs[i];
        x1.limbs[i] ^= b1.limbs[i];
    }
    i = 0;
    inline while (i < 5) : (i += 1) {
        x0.limbs[i] &= mask;
        x1.limbs[i] &= mask;
    }
    i = 0;
    inline while (i < 5) : (i += 1) {
        a0.limbs[i] ^= x0.limbs[i];
        b0.limbs[i] ^= x0.limbs[i];
        a1.limbs[i] ^= x1.limbs[i];
        b1.limbs[i] ^= x1.limbs[i];
    }
}  