Method LeftShiftAny

postgres/parser/utils/bitarray.go:226–274

LeftShiftAny performs a logical left shift, with a possible negative count. The number of bits to shift can be arbitrarily large (i.e. possibly larger than 64 in absolute value).

(n int64)

// The number of bits to shift can be arbitrarily large (i.e. possibly
// larger than 64 in absolute value).
func (d BitArray) LeftShiftAny(n int64) BitArray {
	bitlen := d.BitLen()
	if n == 0 || bitlen == 0 {
		// Fast path.
		return d
	}

	r := MakeZeroBitArray(bitlen)
	if (n > 0 && n > int64(bitlen)) || (n < 0 && -n > int64(bitlen)) {
		// Fast path.
		return r
	}

	if n > 0 {
		// This is a left shift.
		dstWord := uint(0)
		srcWord := uint(uint64(n) / numBitsPerWord)
		srcShift := uint(uint64(n) % numBitsPerWord)
		for i, j := srcWord, dstWord; i < uint(len(d.words)); i++ {
			r.words[j] = d.words[i] << srcShift
			j++
		}
		for i, j := srcWord+1, dstWord; i < uint(len(d.words)); i++ {
			r.words[j] |= d.words[i] >> (numBitsPerWord - srcShift)
			j++
		}
	} else {
		// A right shift.
		n = -n
		srcWord := uint(0)
		dstWord := uint(uint64(n) / numBitsPerWord)
		srcShift := uint(uint64(n) % numBitsPerWord)
		for i, j := srcWord, dstWord; j < uint(len(r.words)); i++ {
			r.words[j] = d.words[i] >> srcShift
			j++
		}
		for i, j := srcWord, dstWord+1; j < uint(len(r.words)); i++ {
			r.words[j] |= d.words[i] << (numBitsPerWord - srcShift)
			j++
		}
		// Erase the trailing bits that are not used any more.
		// See #36606.
		if len(r.words) > 0 {
			r.words[len(r.words)-1] &= ^word(0) << (numBitsPerWord - r.lastBitsUsed)
		}
	}

	return r
}

// byteReprs contains the bit representation of the 256 possible
// groups of 8 bits.