Ejemplo n.º 1
0
// Pack a floating point value change for placement into a uint64 "bit-stream"
//
// If there is no change, packed value is a one-bit long value of 0
// If there is change, packed value is a variable-length bit value:
//	1-bits - Set to 1
//	5-bits - Number of leading zeros in XOR of fPrev and fCurr
//	6-bits - Length of significant bits of XOR of fPrev and fCurr
//	X-bits - Value of XOR of fPrev and fCurr
//
// Packed value is returned such that the LSB of packed value starts at bit 0
// (that is, the packed value is shifted such that there are a bunch of leading
// zeros in the MSB before the first bit, which is set to 1 in the case of a change)
func valuePack(fPrev, fCurr float32) (length uint, packed uint64) {
	xorval := (*(*uint32)(unsafe.Pointer(&fPrev))) ^ (*(*uint32)(unsafe.Pointer(&fCurr)))

	if xorval == 0 {
		return 1, 0
	}

	leadzeroLen := countLeadingZero32(xorval)
	trailzeroLen := countTrailingZero32(xorval)
	sigbitLen := 32 - (leadzeroLen + trailzeroLen)

	packed, _ = bitopts.SetBit64(packed, 63)
	packed, _ = bitopts.SetField64(packed, 62, 58, uint64(leadzeroLen))
	packed, _ = bitopts.SetField64(packed, 57, 52, uint64(sigbitLen))
	packed, _ = bitopts.SetField64(packed, 51, 51-(sigbitLen-1), uint64(xorval)>>trailzeroLen)

	packLen := sigbitLen + 12

	return packLen, packed >> (64 - packLen)
}
Ejemplo n.º 2
0
func (vp *bitPacker) Add(length uint, value uint64) {
	lowbit := int64(vp.currentBit) - (int64(length) - 1)
	if lowbit < 0 {
		sr := uint64(length) - (uint64(vp.currentBit) + 1)
		fieldVal := value >> sr
		vp.array[vp.currentIdx], _ = bitopts.SetField64(vp.array[vp.currentIdx], vp.currentBit, 0, uint64(fieldVal))
		vp.array = append(vp.array, uint64(value<<(64-sr)))
		vp.currentBit = 63 - uint(sr)
		vp.currentIdx++
	} else {
		vp.array[vp.currentIdx], _ = bitopts.SetField64(vp.array[vp.currentIdx], vp.currentBit, uint(lowbit), value)
		if lowbit == 0 {
			vp.array = append(vp.array, uint64(0))
			vp.currentBit = 63
			vp.currentIdx++
		} else {
			vp.currentBit = uint(lowbit) - 1
		}
	}
}
Ejemplo n.º 3
0
func timePack(deltaSample, tPrev, tCurr int64) (length uint, packed uint64) {
	tDelta := tCurr - tPrev
	packVal := tDelta - deltaSample

	if packVal == 0 {
		return 1, 0
	}

	if packVal >= -31 && packVal <= 31 {
		packed, _ = bitopts.SetBit64(packed, 63)
		if packVal < 0 {
			packVal = -packVal
			packed, _ = bitopts.SetBit64(packed, 62)
		}
		packed, _ = bitopts.SetField64(packed, 61, 57, uint64(packVal))
	} else {
		panic("unable to pack time")
	}

	return 7, packed >> (64 - 7)
}