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refactor(vm): extract polyphony bitmask calculation to its own function & document better

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This commit is contained in:
vsariola 2021-03-10 09:34:23 +02:00
parent 43ef6fa72c
commit f9225d70a9
1 changed files with 26 additions and 10 deletions
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36
vm/bytepatch.go
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@ -7,6 +7,17 @@ import (
"github.com/vsariola/sointu"
)
// BytePatch is the compiler Sointu VM bytecode & data (delay times, sample
// offsets) ready to interpret or from which the ASM/WASM code can be generate.
//
// PolyphonyBitmask is a rather peculiar bitmask used by Sointu VM to store the
// information about which voices use which instruments: bit MAXVOICES - n - 1
// corresponds to voice n. If the bit 1, the next voice uses the same
// instrument. If the bit 0, the next voice uses different instrument. For
// example, if first instrument has 3 voices, second instrument has 2 voices,
// and third instrument four voices, the PolyphonyBitmask is:
//
// (MSB) 110101110 (LSB)
type BytePatch struct {
Commands []byte
Values []byte
@ -23,7 +34,10 @@ type SampleOffset struct {
}
func Encode(patch sointu.Patch, featureSet FeatureSet) (*BytePatch, error) {
var c BytePatch
c := BytePatch{PolyphonyBitmask: polyphonyBitmask(patch), NumVoices: uint32(patch.NumVoices())}
if c.NumVoices > 32 {
return nil, fmt.Errorf("Sointu does not support more than 32 concurrent voices; patch uses %v", c.NumVoices)
}
sampleOffsetMap := map[SampleOffset]int{}
globalAddrs := map[int]uint16{}
globalFixups := map[int]([]int){}
@ -175,19 +189,21 @@ func Encode(patch sointu.Patch, featureSet FeatureSet) (*BytePatch, error) {
}
c.Commands = append(c.Commands, byte(0)) // advance
voiceNo += instr.NumVoices
c.NumVoices += uint32(instr.NumVoices)
for k := 0; k < instr.NumVoices-1; k++ {
c.PolyphonyBitmask = (c.PolyphonyBitmask << 1) + 1
}
c.PolyphonyBitmask <<= 1
}
if c.NumVoices > 32 {
return nil, fmt.Errorf("Sointu does not support more than 32 concurrent voices; patch uses %v", c.NumVoices)
}
return &c, nil
}
func polyphonyBitmask(patch sointu.Patch) uint32 {
var ret uint32 = 0
for _, instr := range patch {
for j := 0; j < instr.NumVoices-1; j++ {
ret = (ret << 1) + 1 // for each instrument, NumVoices - 1 bits are ones
}
ret <<= 1 // ...and the last bit is zero, to denote "change instrument"
}
return ret
}
func fixUp(values []byte, positions []int, delta uint16) {
for _, pos := range positions {
orig := (uint16(values[pos+1]) << 8) + uint16(values[pos])