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_cbsearch.go

@@ -0,0 +1,85 @@
+package amrnb
+
+// Algebraic-codebook search infrastructure, ported from opencore-amrnb
+// cor_h_x.cpp (cor_h_x) and set_sign.cpp (set_sign). corHX computes the
+// backward correlation dn[] between the search target and the weighted impulse
+// response (the gradient that drives pulse placement); setSign extracts the
+// per-position pulse signs and prunes each track to its strongest candidate
+// positions. These feed the per-mode pulse searches. Bit-exact with the
+// reference.
+
+const (
+	cNB_TRACK = 5 // number of pulse tracks
+	cSTEP     = 5 // codebook track step
+)
+
+// corHX computes dn[i] = normalized 2·sum_j x[i+j]·h[j], the correlation between
+// the target x and the impulse response h, scaled so it fits 16 bits (sf is the
+// scaling factor: 2 for 12.2k, 1 otherwise). Mirrors cor_h_x.
+func corHX(h, x, dn []int16, sf int16) {
+	// y32[i] = 2·sum_{j=0}^{L-1-i} x[i+j]·h[j]. Zero-padding x past L makes the
+	// out-of-range taps contribute 0, so the whole set of positions is one L-tap
+	// FIR over the padded input (firRaw). The per-term <<1 distributes over the
+	// wrapping sum, so dst[i]<<1 is bit-identical to the per-term shift.
+	var xpad [2 * cL_CODE]int16
+	copy(xpad[:cL_CODE], x[:cL_CODE])
+	var dst [cL_CODE]int32
+	firRaw(dst[:], xpad[:], h[:cL_CODE])
+
+	var y32 [cL_CODE]int32
+	for i := 0; i < cL_CODE; i++ {
+		y32[i] = dst[i] << 1
+	}
+
+	tot := int32(5)
+	for k := 0; k < cNB_TRACK; k++ {
+		var max int32
+		for i := k; i < cL_CODE; i += cSTEP {
+			s := y32[i]
+			if s < 0 {
+				s = -s
+			}
+			if s > max {
+				max = s
+			}
+		}
+		tot += max >> 1
+	}
+
+	j := norm_l(tot) - sf
+	for i := 0; i < cL_CODE; i++ {
+		s := L_shl(y32[i], j)
+		dn[i] = int16((s + 0x8000) >> 16)
+	}
+}
+
+// setSign records the sign of each dn[] entry (±32767), takes |dn|, and prunes
+// dn2[] to keep only the n strongest positions per track (the rest set to -1).
+// Mirrors set_sign.
+func setSign(dn, sign, dn2 []int16, n int16) {
+	for i := 0; i < cL_CODE; i++ {
+		val := dn[i]
+		if val >= 0 {
+			sign[i] = 32767
+		} else {
+			sign[i] = -32767
+			val = negate(val)
+		}
+		dn[i] = val
+		dn2[i] = val
+	}
+
+	for i := 0; i < cNB_TRACK; i++ {
+		for k := int16(0); k < 8-n; k++ {
+			min := int16(0x7fff)
+			pos := i
+			for j := i; j < cL_CODE; j += cSTEP {
+				if dn2[j] >= 0 && dn2[j] < min {
+					min = dn2[j]
+					pos = j
+				}
+			}
+			dn2[pos] = -1
+		}
+	}
+}