51 lines
1.7 KiB
Go
51 lines
1.7 KiB
Go
package amrnb
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// Encoder-side bit serialization, ported from opencore-amrnb prm2bits.cpp
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// (Int2bin/Prm2bits) and the ETS->IETF reordering in ets_to_wmf.cpp
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// (ets_to_ietf). The chain is: parameter array -> ETS serial bits (each
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// parameter expanded MSB-first to its bitno width) -> IETF storage bytes (the
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// ETS bits permuted by reorderBits and packed MSB-first). The leading ToC byte
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// is added by the payload layer, not here.
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// int2bin writes the low nBits of value into bits[0:nBits], MSB first
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// (bits[0] is the most significant bit). Mirrors Int2bin.
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func int2bin(value int16, nBits int, bits []int16) {
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for i := nBits - 1; i >= 0; i-- {
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bits[i] = value & 1
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value >>= 1
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}
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}
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// prm2bits expands the encoder parameter array prm into the ETS serial bit
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// array for the given speech mode (length modeBits[mode]). Mirrors Prm2bits.
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func prm2bits(mode Mode, prm []int16) []int16 {
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bn := bitno[mode]
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ets := make([]int16, modeBits[mode])
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pos := 0
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for i, w := range bn {
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int2bin(prm[i], int(w), ets[pos:])
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pos += int(w)
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}
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return ets
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}
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// etsToIetf permutes the ETS serial bits into IETF storage order via
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// reorderBits[mode] and packs them MSB-first into bytes. Mirrors the speech
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// branch of ets_to_ietf (without the ToC byte).
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func etsToIetf(mode Mode, ets []int16) []byte {
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nb := modeBits[mode]
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ro := reorderBits[mode]
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out := make([]byte, (nb+7)/8)
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for k := 0; k < nb; k++ {
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bit := ets[ro[k]] & 1
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out[k>>3] |= byte(bit) << uint(7-(k&7))
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}
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return out
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}
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// packFrame serializes a mode's encoder parameters into the RFC 4867 speech
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// payload bytes (IETF storage order), the inverse of mimeUnsort.
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func packFrame(prm []int16, mode Mode) []byte {
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return etsToIetf(mode, prm2bits(mode, prm))
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}
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