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91 lines
2.1 KiB
Go
91 lines
2.1 KiB
Go
package ent
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import (
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"math"
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"github.com/jordanorelli/hyperstone/bit"
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)
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const (
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f_min = 1 << iota
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f_max
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f_center
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)
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func floatDecoder(f *Field) decoder {
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if f.encoder != nil && f.encoder.String() == "coord" {
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return nil
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}
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if f.bits <= 0 || f.bits >= 32 {
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return ieeeFloat32Decoder
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}
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// a quantized field value must have some range specified, otherwise the
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// quantization makes no sense.
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if f.low == 0 && f.high == 0 {
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panic("quantization rules make no sense")
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}
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bits := f.bits
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low := f.low
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high := f.high
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flags := f.flags
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// there's a flag that's -8 and i don't know what to do with it. I'm just
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// gonna mask away everything except the three least significant bits and
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// pray for the best.
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flags = flags & 7
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// number of input steps
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steps := int(1<<f.bits - 1)
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// keep the inverse to mult instead of divide later
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inv_steps := 1.0 / float32(steps)
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// total range of values
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span := f.high - f.low
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if span < 0 {
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panic("quantization span is backwards")
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}
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// output width of each step
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step_width := span * inv_steps
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var special *float32
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switch {
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case flags&f_min > 0:
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special = new(float32)
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*special = low
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case flags&f_max > 0:
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special = new(float32)
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*special = high
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case flags&f_center > 0:
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special = new(float32)
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middle := (high + low) * 0.5
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// if we're within a step of zero just return zero.
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if middle > 0 && middle-step_width < 0 || middle < 0 && middle+step_width > 0 {
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middle = 0
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}
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*special = middle
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}
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return func(br bit.Reader) interface{} {
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if special != nil && bit.ReadBool(br) {
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Debug.Printf("decode float type: %s low: %f high: %f bits: %d steps: %d span: %f flags: %d special: %v", f._type.String(), low, high, bits, steps, span, flags, *special)
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return *special
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}
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u := br.ReadBits(bits)
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out := low + float32(u)*inv_steps*span
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Debug.Printf("decode float type: %s low: %f high: %f bits: %d bitVal: %d steps: %d span: %f flags: %d output: %v", f._type.String(), low, high, bits, u, steps, span, flags, out)
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return out
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}
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}
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// reads an IEEE 754 binary float value off of the stream
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func ieeeFloat32Decoder(br bit.Reader) interface{} {
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return math.Float32frombits(uint32(br.ReadBits(32)))
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}
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