func testChunkDiff(t *testing.T, a, b *chunk) {
if a.ctx != b.ctx {
panic("chunks with different contexts")
}
bitsDiff := 0
for i := uint32(0); i < a.ctx.chunkSize; i++ {
bitsDiff += int(swar.Ones8(a.data[i] ^ b.data[i]))
}
if bitsDiff != 1 {
t.Errorf("%#v and %#v differ by more than 1 bit (by %v)", a.data, b.data, bitsDiff)
}
}
// readBitMask xors the bits specified out of the byte B by applying the
// mask and then stores the value in the atom a at the specified atom
// bit index abi.
func (c *chunk) readBitMask(a *atom, abi uint8, mask byte, B byte) {
// First, extract the desired bits from the chunk byte by using
// the mask.
x := mask & B
// We then want to XOR together the bits specified by the mask.
// The key is to recognize that this is the same as taking the
// 8-bit population count (ones count, or Hamming weight) and
// then examining the parity. If even, then 0; if odd, then 1.
x = swar.Ones8(x) % 2
// XOR the bit into the atom.
a.xorBit(x, abi)
// Done!
}
func testBytesDiff(t *testing.T, a, b []byte, expectBits int) {
var m int
if len(a) < len(b) {
m = len(a)
} else {
m = len(b)
}
bitsDiff := 0
for i := 0; i < m; i++ {
bitsDiff += int(swar.Ones8(a[i] ^ b[i]))
}
if bitsDiff != expectBits {
t.Errorf("not %v bit difference (is %v)", expectBits, bitsDiff)
}
}
