lavc/flacdsp: R-V Zvl256b lpc33

flac_lpc_33_13_c: 499.7
flac_lpc_33_13_rvv_i64: 197.7
flac_lpc_33_16_c: 601.5
flac_lpc_33_16_rvv_i64: 195.2
flac_lpc_33_29_c: 1011.5
flac_lpc_33_29_rvv_i64: 300.7
flac_lpc_33_32_c: 1099.0
flac_lpc_33_32_rvv_i64: 296.7

libavcodec/riscv/flacdsp_init.c

@@ -31,6 +31,8 @@ void ff_flac_lpc32_rvv(int32_t *decoded, const int coeffs[32],
                        int pred_order, int qlevel, int len);
 void ff_flac_lpc32_rvv_simple(int32_t *decoded, const int coeffs[32],
                               int pred_order, int qlevel, int len);
+void ff_flac_lpc33_rvv(int64_t *, const int32_t *, const int coeffs[32],
+                       int pred_order, int qlevel, int len);
 void ff_flac_wasted32_rvv(int32_t *, int shift, int len);
 void ff_flac_wasted33_rvv(int64_t *, const int32_t *, int shift, int len);
 void ff_flac_decorrelate_indep2_16_rvv(uint8_t **out, int32_t **in,
@@ -76,9 +78,10 @@ av_cold void ff_flacdsp_init_riscv(FLACDSPContext *c, enum AVSampleFormat fmt,
 
 # if (__riscv_xlen >= 64)
             if (flags & AV_CPU_FLAG_RVV_I64) {
-                if (vlenb > 16)
+                if (vlenb > 16) {
                     c->lpc32 = ff_flac_lpc32_rvv_simple;
-                else
+                    c->lpc33 = ff_flac_lpc33_rvv;
+                } else
                     c->lpc32 = ff_flac_lpc32_rvv;
             }
 # endif

libavcodec/riscv/flacdsp_rvv.S

@@ -103,6 +103,33 @@ func ff_flac_lpc32_rvv_simple, zve64x, zbb
 
         ret
 endfunc
+
+func ff_flac_lpc33_rvv, zve64x, zbb
+        vtype_vli t0, a3, t1, e64, ta, ma
+        vsetvl  zero, a3, t0
+        vmv.s.x v0, zero
+        sh2add  a1, a3, a1
+        vle32.v v24, (a2)
+        sub     a5, a5, a3
+        vle64.v v16, (a0)
+        sh3add  a0, a3, a0
+        vsext.vf2 v8, v24
+1:
+        vmul.vv v24, v8, v16
+        lw      t0, (a1)
+        addi    a1, a1, 4
+        vredsum.vs v24, v24, v0
+        addi    a5, a5, -1
+        vmv.x.s t1, v24
+        sra     t1, t1, a4
+        add     t0, t0, t1
+        vslide1down.vx v16, v16, t0
+        sd      t0, (a0)
+        addi    a0, a0, 8
+        bnez    a5, 1b
+
+        ret
+endfunc
 #endif
 
 func ff_flac_wasted32_rvv, zve32x