// 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)
}
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
}
}
}
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)
}