feat(capability): 转码能力包（vendor 纯 Go AMR-NB 解码器 + 黄金向量逐样本对照 + 8 哨兵 + 注册面）

internal/capability/transcode/amrnb/dsp_enc_qgainp.go

@@ -0,0 +1,99 @@
+package amrnb
+
+// Separate pitch/code gain quantizers (MR122; pitch also used by MR795), ported
+// from opencore-amrnb q_gain_p.cpp (q_gain_pitch) and q_gain_c.cpp
+// (q_gain_code). qGainPitch picks the nearest quantized pitch gain; qGainCode
+// picks the code-gain index minimizing the error to the predicted gain. The
+// exact encoder counterparts of dGainPitch / dGainCode. Bit-exact with the
+// reference.
+
+const (
+	cNB_QUA_PITCH = 16
+	cNB_QUA_CODE  = 32
+)
+
+// qGainPitch quantizes the pitch gain (in place) to the nearest table entry
+// within gpLimit, returning the index. For MR795 it also fills three candidate
+// gains/indices. Mirrors q_gain_pitch.
+func qGainPitch(mode int, gpLimit int16, gain *int16, gainCand, gainCind []int16) int16 {
+	errMin := abs_s(sub(*gain, qua_gain_pitch[0]))
+	index := int16(0)
+	for i := int16(1); i < cNB_QUA_PITCH; i++ {
+		if qua_gain_pitch[i] <= gpLimit {
+			err := abs_s(sub(*gain, qua_gain_pitch[i]))
+			if err < errMin {
+				errMin = err
+				index = i
+			}
+		}
+	}
+
+	if mode == dMR795 {
+		var ii int16
+		switch {
+		case index == 0:
+			ii = index
+		case index == cNB_QUA_PITCH-1 || qua_gain_pitch[index+1] > gpLimit:
+			ii = index - 2
+		default:
+			ii = index - 1
+		}
+		for i := 0; i < 3; i++ {
+			gainCind[i] = ii
+			gainCand[i] = qua_gain_pitch[ii]
+			ii++
+		}
+		*gain = qua_gain_pitch[index]
+	} else if mode == dMR122 {
+		*gain = qua_gain_pitch[index] &^ 3
+	} else {
+		*gain = qua_gain_pitch[index]
+	}
+	return index
+}
+
+// qGainCode quantizes the fixed-codebook gain (in place) against the predicted
+// gain, returning the index and the predictor-update energies. Mirrors
+// q_gain_code.
+func qGainCode(mode int, expGcode0, fracGcode0 int16, gain *int16) (index, quaEnerMR122, quaEner int16) {
+	var gQ0 int16
+	if mode == dMR122 {
+		gQ0 = *gain >> 1 // Q1 -> Q0
+	} else {
+		gQ0 = *gain
+	}
+
+	gcode0 := int16(pow2(expGcode0, fracGcode0))
+	if mode == dMR122 {
+		gcode0 = shl(gcode0, 4)
+	} else {
+		gcode0 = shl(gcode0, 5)
+	}
+
+	errMin := gQ0 - int16((int32(gcode0)*int32(qua_gain_code[0]))>>15)
+	if errMin < 0 {
+		errMin = -errMin
+	}
+	index = 0
+	for i := int16(1); i < cNB_QUA_CODE; i++ {
+		err := gQ0 - int16((int32(gcode0)*int32(qua_gain_code[i*3]))>>15)
+		if err < 0 {
+			err = -err
+		}
+		if err < errMin {
+			errMin = err
+			index = i
+		}
+	}
+
+	p := int(index) * 3
+	temp := int16((int32(gcode0) * int32(qua_gain_code[p])) >> 15)
+	if mode == dMR122 {
+		*gain = temp << 1
+	} else {
+		*gain = temp
+	}
+	quaEnerMR122 = qua_gain_code[p+1]
+	quaEner = qua_gain_code[p+2]
+	return
+}