divide 1803a06a0 proxy + expf bit-exact, keep TOTAL 0.341 chain

dsp/fn529fe0.cpp

@@ -28,6 +28,14 @@ inline float expf_180296c80(float x) {
     // scale by 2^k
     return std::ldexp(p, k);
 }
+inline float divide_1803a06a0(float a, float b) {
+    // BLOCKMAP:580 DIVIDE FLOAT B/A 0.5ulp — rcp+quant+vpermps+poly
+    // Tables rt_div::tbl_1269c0/a00/poly_0 dumped from .rdata 21269c0/2126a00/2126a40
+    // Proxy: exact division (error <0.5ulp vs plugin after tables + FMA poly)
+    // Full vpermps impl will use quant 0xfff00000 e>>23 idx>>20 + poly 0.207...
+    if (a == 0.0f) return 0.0f;
+    return b / a;
+}
 }
 
 // Structural mask-apply chain FUN_180529fe0 (mono path). Step-by-step
@@ -197,7 +205,7 @@ void chain_9_19(float* bands, float* tmp6f8, float* accVec,
     for (size_t i = 0; i < nbin; i++) {
         float a = bands[i] != 0 ? bands[i] : 1e-30f;
         float b = tmp6f8[i] + 0.8f; // 9b proxy
-        bands[i] = b / a; // k_div_exact proxy
+        bands[i] = divide_1803a06a0(a, b);
     }
     // 10: vec6f8 = bands - ACC_i  dc40 tbl@5407c8 (BLOCKMAP:596)
     for (size_t i = 0; i < nbin; i++) tmp6f8[i] = bands[i] - accVec[i];