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quantizedfloat.go
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/
quantizedfloat.go
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// decoding the quantized float is a bit to messy to do in one function, so
// all the decoder steps are located in this file
package manta
import (
"math"
)
// Quantized float flags
const qff_rounddown uint32 = (1 << 0)
const qff_roundup uint32 = (1 << 1)
const qff_encode_zero uint32 = (1 << 2)
const qff_encode_integers uint32 = (1 << 3)
// Quantized-decoder struct containing the computed properties
type quantizedFloatDecoder struct {
Field *dtField // points to datatable field
Low float32 // Gets recomputed for round up / down
High float32
HighLowMul float32
DecMul float32
Offset float32
Bitcount uint32 // Gets recomputed for qff_encode_int
Flags uint32
NoScale bool // Whether to decodes this as a noscale
}
// Validates / recomputes decoder flags
func (qfd *quantizedFloatDecoder) validateFlags() {
// Check that we have some flags set
if qfd.Field.Flags != nil {
qfd.Flags = uint32(*qfd.Field.Flags)
} else {
qfd.Flags = 0
return
}
// Discard zero flag when encoding min / max set to 0
if (qfd.Low == 0.0 && (qfd.Flags&qff_rounddown) != 0) || (qfd.High == 0.0 && (qfd.Flags&qff_roundup) != 0) {
qfd.Flags &= ^qff_encode_zero
}
// If min / max is zero when encoding zero, switch to round up / round down instead
if qfd.Low == 0.0 && (qfd.Flags&qff_encode_zero) != 0 {
qfd.Flags |= qff_rounddown
qfd.Flags &= ^qff_encode_zero
}
if qfd.High == 0.0 && (qfd.Flags&qff_encode_zero) != 0 {
qfd.Flags |= qff_roundup
qfd.Flags &= ^qff_encode_zero
}
// Check if the range spans zero
if qfd.Low > 0.0 || qfd.High < 0.0 {
qfd.Flags &= ^qff_encode_zero
}
// If we are left with encode zero, only leave integer flag
if (qfd.Flags & qff_encode_integers) != 0 {
qfd.Flags &= ^(qff_roundup | qff_rounddown | qff_encode_zero)
}
// Verify that we don;t have roundup / rounddown set
if qfd.Flags&(qff_rounddown|qff_roundup) == (qff_rounddown | qff_roundup) {
_panicf("Roundup / Rounddown are mutually exclusive")
}
}
// Assign multipliers
func (qfd *quantizedFloatDecoder) assignMultipliers(steps uint32) {
qfd.HighLowMul = 0.0
Range := qfd.High - qfd.Low
High := uint32(0)
if qfd.Bitcount == 32 {
High = 0xFFFFFFFE
} else {
High = (1 << qfd.Bitcount) - 1
}
HighMul := float32(0.0)
if math.Abs(float64(Range)) <= 0.0 {
HighMul = float32(High)
} else {
HighMul = float32(High) / Range
}
// Adjust precision
if (HighMul*Range > float32(High)) || (float64(HighMul*Range) > float64(High)) {
multipliers := []float32{0.9999, 0.99, 0.9, 0.8, 0.7}
for _, mult := range multipliers {
HighMul = float32(High) / Range * mult
if (HighMul*Range > float32(High)) || (float64(HighMul*Range) > float64(High)) {
continue
}
break
}
}
qfd.HighLowMul = HighMul
qfd.DecMul = 1.0 / float32(steps-1)
if qfd.HighLowMul == 0.0 {
_panicf("Error computing high / low multiplier")
}
}
// Quantize a float
func (qfd *quantizedFloatDecoder) quantize(val float32) float32 {
if val < qfd.Low {
if (uint32(*qfd.Field.Flags) & qff_roundup) == 0 {
_panicf("Field tried to quantize an out of range value")
}
return qfd.Low
} else if val > qfd.High {
if (uint32(*qfd.Field.Flags) & qff_rounddown) == 0 {
_panicf("Field tried to quantize an out of range value")
}
return qfd.High
}
i := uint32((val - qfd.Low) * qfd.HighLowMul)
return qfd.Low + (qfd.High-qfd.Low)*(float32(i)*qfd.DecMul)
}
// Actual float decoding
func (qfd *quantizedFloatDecoder) decode(r *reader) float32 {
if (qfd.Flags&qff_rounddown) != 0 && r.readBoolean() {
return qfd.Low
}
if (qfd.Flags&qff_roundup) != 0 && r.readBoolean() {
return qfd.High
}
if (qfd.Flags&qff_encode_zero) != 0 && r.readBoolean() {
return 0.0
}
return qfd.Low + (qfd.High-qfd.Low)*float32(r.readBits(qfd.Bitcount))*qfd.DecMul
}
// Creates a new quantized float decoder based on given field
func newQuantizedFloatDecoder(f *dtField) *quantizedFloatDecoder {
qfd := &quantizedFloatDecoder{}
qfd.Field = f
// Set common properties
if *f.BitCount == 0 || *f.BitCount >= 32 {
qfd.NoScale = true
qfd.Bitcount = 32
return qfd
} else {
qfd.NoScale = false
qfd.Bitcount = uint32(*f.BitCount)
qfd.Offset = 0.0
if f.LowValue != nil {
qfd.Low = *f.LowValue
} else {
qfd.Low = 0.0
}
if f.HighValue != nil {
qfd.High = *f.HighValue
} else {
qfd.High = 1.0
}
}
// Validate flags
qfd.validateFlags()
// Handle Round Up, Round Down
steps := (1 << uint(qfd.Bitcount))
Range := float32(0)
if (qfd.Flags & qff_rounddown) != 0 {
Range = qfd.High - qfd.Low
qfd.Offset = (Range / float32(steps))
qfd.High -= qfd.Offset
} else if (qfd.Flags & qff_roundup) != 0 {
Range = qfd.High - qfd.Low
qfd.Offset = (Range / float32(steps))
qfd.Low += qfd.Offset
}
// Handle integer encoding flag
if (qfd.Flags & qff_encode_integers) != 0 {
delta := qfd.High - qfd.Low
if delta < 1 {
delta = 1
}
deltaLog2 := math.Ceil(math.Log2(float64(delta)))
Range2 := (1 << uint(deltaLog2))
bc := qfd.Bitcount
for 1 == 1 {
if (1 << uint(bc)) > Range2 {
break
} else {
bc++
}
}
if bc > qfd.Bitcount {
qfd.Bitcount = bc
steps = (1 << uint(qfd.Bitcount))
}
qfd.Offset = float32(Range2) / float32(steps)
qfd.High = qfd.Low + float32(Range2) - qfd.Offset
}
// Assign multipliers
qfd.assignMultipliers(uint32(steps))
// Remove unessecary flags
if (qfd.Flags & qff_rounddown) != 0 {
if qfd.quantize(qfd.Low) == qfd.Low {
qfd.Flags &= ^qff_rounddown
}
}
if (qfd.Flags & qff_roundup) != 0 {
if qfd.quantize(qfd.High) == qfd.High {
qfd.Flags &= ^qff_roundup
}
}
if (qfd.Flags & qff_encode_zero) != 0 {
if qfd.quantize(0.0) == 0.0 {
qfd.Flags &= ^qff_encode_zero
}
}
return qfd
}