ARM assembler predictor decoding function. This increases my -c1000 test track from around 94% realtime on an ipod to around 104% realtime, but yields only a tiny speedup (453% to 455%) on the Gigabeat. Including this optimisation, total decoding time for my 245.70s -c1000 test track on an ipod is 236.06s, with the predictor decoding taking 51.40s of that time - meaning the predictor decoding is only about 22% of the total decoding time.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@13626 a1c6a512-1295-4272-9138-f99709370657

4 files changed, 520 insertions, 2 deletions

diff --git a/apps/codecs/demac/libdemac/SOURCES b/apps/codecs/demac/libdemac/SOURCES
index 76b891a90d..c68fff104e 100644
--- a/apps/codecs/demac/libdemac/SOURCES
+++ b/apps/codecs/demac/libdemac/SOURCES
@@ -1,5 +1,8 @@
 crc.c
 predictor.c
+#ifdef CPU_ARM
+predictor-arm.S
+#endif
 entropy.c
 decoder.c
 parser.c
diff --git a/apps/codecs/demac/libdemac/parser.h b/apps/codecs/demac/libdemac/parser.h
index 301cf4a5e1..4ef0977e6b 100644
--- a/apps/codecs/demac/libdemac/parser.h
+++ b/apps/codecs/demac/libdemac/parser.h
@@ -71,6 +71,10 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110, USA
 /* Total size of all predictor histories - 50 * sizeof(int32_t) */
 #define PREDICTOR_SIZE 50
 
+
+/* NOTE: This struct is used in predictor-arm.S - any updates need to
+   be reflected there. */
+
 struct predictor_t
 {
     /* Filter histories */
@@ -79,10 +83,12 @@ struct predictor_t
     int32_t YlastA;
     int32_t XlastA;
 
-    int32_t YfilterA;
-    int32_t XfilterA;
+    /* NOTE: The order of the next four fields is important for
+       predictor-arm.S */
     int32_t YfilterB;
+    int32_t XfilterA;
     int32_t XfilterB;
+    int32_t YfilterA;
 
     /* Adaption co-efficients */
     int32_t YcoeffsA[4];
diff --git a/apps/codecs/demac/libdemac/predictor-arm.S b/apps/codecs/demac/libdemac/predictor-arm.S
new file mode 100644
index 0000000000..1a04b5d66a
--- /dev/null
+++ b/apps/codecs/demac/libdemac/predictor-arm.S
@@ -0,0 +1,507 @@
+/*
+
+libdemac - A Monkey's Audio decoder
+
+$Id: predictor.c 13597 2007-06-08 22:35:26Z dave $
+
+Copyright (C) Dave Chapman 2007
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110, USA
+
+*/
+
+    .section    .text,"ax",%progbits
+
+    .align      2
+
+    .global     predictor_decode_stereo
+    .type       predictor_decode_stereo,%function
+
+
+/* NOTE: The following need to be kept in sync with parser.h */
+
+#define HISTORY_SIZE   512
+
+#define YDELAYA        200
+#define YDELAYB        168
+#define XDELAYA        136
+#define XDELAYB        104
+#define YADAPTCOEFFSA   72
+#define XADAPTCOEFFSA   56
+#define YADAPTCOEFFSB   40
+#define XADAPTCOEFFSB   20
+
+/* struct predictor_t members: */
+#define buf              0    /* int32_t* buf */
+
+#define YlastA           4    /* int32_t YlastA; */
+#define XlastA           8    /* int32_t XlastA; */
+
+#define YfilterB        12    /* int32_t YfilterB; */
+#define XfilterA        16    /* int32_t XfilterA; */
+
+#define XfilterB        20    /* int32_t XfilterB; */
+#define YfilterA        24    /* int32_t YfilterA; */
+        
+#define YcoeffsA        28    /* int32_t YcoeffsA[4]; */
+#define XcoeffsA        44    /* int32_t XcoeffsA[4]; */
+#define YcoeffsB        60    /* int32_t YcoeffsB[5]; */
+#define XcoeffsB        80    /* int32_t XcoeffsB[5]; */
+
+#define historybuffer  100    /* int32_t historybuffer[] */
+
+@ Register usage:
+@
+@ r0-r11 - scratch
+@ r12 - struct predictor_t* p
+@ r14 - int32_t* p->buf
+
+@ void predictor_decode_stereo(struct predictor_t* p,
+@                              int32_t* decoded0,
+@                              int32_t* decoded1,
+@                              int count)
+
+predictor_decode_stereo:
+    stmdb   sp!, {r1-r11, lr}
+
+    @ r1 (decoded0) is [sp]
+    @ r2 (decoded1) is [sp, #4]
+    @ r3 (count)    is [sp, #8]
+
+    mov     r12, r0       @ r12 := p
+    ldr     r14, [r0]     @ r14 := p->buf
+
+loop:
+
+@@@@@@@@@@@@@@@@@@@@@@@@@@@ PREDICTOR Y
+
+@ Predictor Y, Filter A
+
+    ldr     r10, [r12, #YlastA]     @ r10 := p->YlastA
+    add     r11, r14, #YDELAYA-12   @ r11 := &p->buf[YDELAYA-3]
+
+    ldmia   r11, { r2 - r4 }        @ r2 := p->buf[YDELAYA-3]
+                                    @ r3 := p->buf[YDELAYA-2]
+                                    @ r4 := p->buf[YDELAYA-1]
+
+    subs    r4, r10, r4             @ r4 := r10 - r4
+
+    add     r1, r12, #YcoeffsA
+    ldmia   r1, {r6 - r9}           @ r6 := p->YcoeffsA[0]
+                                    @ r7 := p->YcoeffsA[1]
+                                    @ r8 := p->YcoeffsA[2]
+                                    @ r9 := p->YcoeffsA[3]
+
+    mul     r0, r10, r6             @ r0 := p->buf[YDELAYA] * p->YcoeffsA[0]
+    mla     r0, r4, r7, r0          @ r0 += p->buf[YDELAYA-1] * p->YcoeffsA[1]
+    mla     r0, r3, r8, r0          @ r0 += p->buf[YDELAYA-2] * p->YcoeffsA[2]
+    mla     r0, r2, r9, r0          @ r0 += p->buf[YDELAYA-3] * p->YcoeffsA[3]
+
+    add     r11, r14, #YDELAYA-4
+    stmia   r11, { r4, r10 }        @ p->buf[YDELAYA-1] = r4
+                                    @ p->buf[YDELAYA] = r10
+
+    @ flags were set above, in the subs instruction
+    mvngt   r4, #0
+    movlt   r4, #1                  @ r4 := SIGN(r4) (see .c for SIGN macro)
+
+    cmp     r10, #0
+    mvngt   r10, #0
+    movlt   r10, #1                 @ r10 := SIGN(r10) (see .c for SIGN macro)
+
+    add     r1, r14, #YADAPTCOEFFSA-4
+    stmia   r1, {r4, r10}           @ p->buf[YADAPTCOEFFSA-1] := r4
+                                    @ p->buf[YADAPTCOEFFSA] := r10
+
+    @ NOTE: r0 now contains predictionA - don't overwrite.
+
+@ Predictor Y, Filter B
+
+    add     r2, r12, #YfilterB
+    ldmia   r2, {r2, r11}           @ r2 := p->YfilterB
+                                    @ r11 := p->XfilterA
+
+    rsb     r2, r2, r2, lsl #5      @ r2 := r2 * 32 - r2 ( == r2*31)
+    sub     r10, r11, r2, asr #5    @ r10 (p->buf[YDELAYB]) := r11 - (r2 >> 5)
+
+    str     r11, [r12, #YfilterB]   @ p->YfilterB := r11 (p->XfilterA)
+
+    add     r11, r14, #YDELAYB-16   @ r11 := &p->buf[YDELAYB-4]
+
+    ldmia   r11, { r2 - r5 }        @ r2 := p->buf[YDELAYB-4]
+                                    @ r3 := p->buf[YDELAYB-3]
+                                    @ r4 := p->buf[YDELAYB-2]
+                                    @ r5 := p->buf[YDELAYB-1]
+
+    subs    r5, r10, r5             @ r5 := r10 - r5
+
+    add     r1, r12, #YcoeffsB
+    ldmia   r1, {r6,r7,r8,r9,r11}   @ r6 := p->YcoeffsB[0]
+                                    @ r7 := p->YcoeffsB[1]
+                                    @ r8 := p->YcoeffsB[2]
+                                    @ r9 := p->YcoeffsB[3]
+                                    @ r11 := p->YcoeffsB[4]
+
+    mul     r1, r10, r6             @ r1 := p->buf[YDELAYB] * p->YcoeffsB[0]
+    mla     r1, r5, r7, r1          @ r1 += p->buf[YDELAYB-1] * p->YcoeffsB[1]
+    mla     r1, r4, r8, r1          @ r1 += p->buf[YDELAYB-2] * p->YcoeffsB[2]
+    mla     r1, r3, r9, r1          @ r1 += p->buf[YDELAYB-3] * p->YcoeffsB[3]
+    mla     r1, r2, r11, r1         @ r1 += p->buf[YDELAYB-4] * p->YcoeffsB[4]
+
+    add     r2, r14, #YDELAYB-4     @ r2 := &p->buf[YDELAYB-1]
+    stmia   r2, { r5, r10 }         @ p->buf[YDELAYB-1] = r5
+                                    @ p->buf[YDELAYB] = r10
+
+    @ flags were set above, in the subs instruction
+    mvngt   r5, #0
+    movlt   r5, #1                 @ r5 := SIGN(r5) (see .c for SIGN macro)
+
+    cmp     r10, #0
+    mvngt   r10, #0
+    movlt   r10, #1                @ r10 := SIGN(r10) (see .c for SIGN macro)
+
+    add     r2, r14, #YADAPTCOEFFSB-4
+    stmia   r2, {r5, r10}           @ p->buf[YADAPTCOEFFSB-1] := r5
+                                    @ p->buf[YADAPTCOEFFSB] := r10
+
+    @ r0 still contains predictionA
+    @ r1 contains predictionB
+
+    @ Finish Predictor Y
+
+    ldr     r2, [sp]                @ r2 := decoded0
+    add     r0, r0, r1, asr #1      @ r0 := r0 + (r1 >> 1)
+    ldr     r3, [r2]                @ r3 := *decoded0
+    add     r1, r3, r0, asr #10     @ r1 := r3 + (r0 >> 10)
+    str     r1, [r12, #YlastA]      @ p->YlastA := r1
+
+    ldr     r4, [r12, #YfilterA]    @ r4 := p->YfilterA
+    rsb     r4, r4, r4, lsl #5      @ r4 := r4 * 32 - r4 ( == r4*31)
+    add     r1, r1, r4, asr #5      @ r1 := r1 + (r4 >> 5)
+    str     r1, [r12, #YfilterA]    @ p->YfilterA := r1
+
+    @ r1 contains p->YfilterA
+    @ r2 contains decoded0
+    @ r3 contains *decoded0
+
+    @ r6, r7, r8, r9, r11 contain p->YcoeffsB[0..4]
+    @ r5, r10 contain p->buf[YADAPTCOEFFSB-1] and p->buf[YADAPTCOEFFSB]
+
+    cmp     r3, #0
+    stmia   r2!, {r1}               @ *(decoded0++) := r1  (p->YfilterA)
+    str     r2, [sp]                @ save decoded0
+    beq     2f
+
+    add     r1, r14, #YADAPTCOEFFSB-16
+    ldmia   r1, { r2, r3, r4 }      @ r2 := p->buf[YADAPTCOEFFSB-4]
+                                    @ r3 := p->buf[YADAPTCOEFFSB-3]
+                                    @ r4 := p->buf[YADAPTCOEFFSB-2]
+    blt     1f
+
+    @ *decoded0 > 0
+
+    sub     r6, r6, r10       @ r6 := p->YcoeffsB[0] - p->buf[YADAPTCOEFFSB]
+    sub     r7, r7, r5        @ r7 := p->YcoeffsB[1] - p->buf[YADAPTCOEFFSB-1]
+    sub     r8, r8, r4        @ r8 := p->YcoeffsB[2] - p->buf[YADAPTCOEFFSB-2]
+    sub     r9, r9, r3        @ r9 := p->YcoeffsB[3] - p->buf[YADAPTCOEFFSB-3]
+    sub     r11, r11, r2      @ r11 := p->YcoeffsB[4] - p->buf[YADAPTCOEFFSB-4]
+
+    add     r0, r12, #YcoeffsB      
+    stmia   r0, {r6,r7,r8,r9,r11}   @ Save p->YcoeffsB[]
+
+    add     r1, r12, #YcoeffsA
+    ldmia   r1, { r2-r5 }           @ r2 := p->YcoeffsA[0]
+                                    @ r3 := p->YcoeffsA[1]
+                                    @ r4 := p->YcoeffsA[2]
+                                    @ r5 := p->YcoeffsA[3]
+
+    add     r0, r14, #YADAPTCOEFFSA-12
+    ldmia   r0, { r6-r9}            @ r6 := p->buf[YADAPTCOEFFSA-3]
+                                    @ r7 := p->buf[YADAPTCOEFFSA-2]
+                                    @ r8 := p->buf[YADAPTCOEFFSA-1]
+                                    @ r9 := p->buf[YADAPTCOEFFSA]
+
+    sub     r2, r2, r9        @ r2 := p->YcoeffsA[0] - p->buf[YADAPTCOEFFSA]
+    sub     r3, r3, r8        @ r3 := p->YcoeffsA[1] - p->buf[YADAPTCOEFFSA-1]
+    sub     r4, r4, r7        @ r4 := p->YcoeffsA[2] - p->buf[YADAPTCOEFFSA-2]
+    sub     r5, r5, r6        @ r5 := p->YcoeffsA[3] - p->buf[YADAPTCOEFFSA-3]
+    
+    stmia   r1, {r2-r5}             @ Save p->YcoeffsA
+    b       2f
+
+
+1:  @ *decoded0 < 0
+
+    add     r6, r6, r10       @ r6 := p->YcoeffsB[0] + p->buf[YADAPTCOEFFSB]
+    add     r7, r7, r5        @ r7 := p->YcoeffsB[1] + p->buf[YADAPTCOEFFSB-1]
+    add     r8, r8, r4        @ r8 := p->YcoeffsB[2] + p->buf[YADAPTCOEFFSB-2]
+    add     r9, r9, r3        @ r9 := p->YcoeffsB[3] + p->buf[YADAPTCOEFFSB-3]
+    add     r11, r11, r2      @ r11 := p->YcoeffsB[4] + p->buf[YADAPTCOEFFSB-4]
+
+    add     r0, r12, #YcoeffsB      
+    stmia   r0, {r6,r7,r8,r9,r11}   @ Save p->YcoeffsB[]
+
+    add     r1, r12, #YcoeffsA
+    ldmia   r1, { r2-r5 }           @ r2 := p->YcoeffsA[0]
+                                    @ r3 := p->YcoeffsA[1]
+                                    @ r4 := p->YcoeffsA[2]
+                                    @ r5 := p->YcoeffsA[3]
+
+    add     r0, r14, #YADAPTCOEFFSA-12
+    ldmia   r0, { r6-r9}            @ r6 := p->buf[YADAPTCOEFFSA-3]
+                                    @ r7 := p->buf[YADAPTCOEFFSA-2]
+                                    @ r8 := p->buf[YADAPTCOEFFSA-1]
+                                    @ r9 := p->buf[YADAPTCOEFFSA]
+
+    add     r2, r2, r9        @ r2 := p->YcoeffsA[0] + p->buf[YADAPTCOEFFSA]
+    add     r3, r3, r8        @ r3 := p->YcoeffsA[1] + p->buf[YADAPTCOEFFSA-1]
+    add     r4, r4, r7        @ r4 := p->YcoeffsA[2] + p->buf[YADAPTCOEFFSA-2]
+    add     r5, r5, r6        @ r5 := p->YcoeffsA[3] + p->buf[YADAPTCOEFFSA-3]
+    
+    stmia   r1, {r2-r5}       @ Save p->YcoeffsA
+
+2:
+
+@@@@@@@@@@@@@@@@@@@@@@@@@@@ PREDICTOR X
+
+@ Predictor X, Filter A
+
+    ldr     r10, [r12, #XlastA]     @ r10 := p->XlastA
+    add     r11, r14, #XDELAYA-12   @ r11 := &p->buf[XDELAYA-3]
+
+    ldmia   r11, { r2 - r4 }        @ r2 := p->buf[XDELAYA-3]
+                                    @ r3 := p->buf[XDELAYA-2]
+                                    @ r4 := p->buf[XDELAYA-1]
+
+    subs    r4, r10, r4             @ r4 := r10 - r4
+
+    add     r1, r12, #XcoeffsA
+    ldmia   r1, {r6 - r9}           @ r6 := p->XcoeffsA[0]
+                                    @ r7 := p->XcoeffsA[1]
+                                    @ r8 := p->XcoeffsA[2]
+                                    @ r9 := p->XcoeffsA[3]
+
+    mul     r0, r10, r6             @ r0 := p->buf[XDELAYA] * p->XcoeffsA[0]
+    mla     r0, r4, r7, r0          @ r0 += p->buf[XDELAYA-1] * p->XcoeffsA[1]
+    mla     r0, r3, r8, r0          @ r0 += p->buf[XDELAYA-2] * p->XcoeffsA[2]
+    mla     r0, r2, r9, r0          @ r0 += p->buf[XDELAYA-3] * p->XcoeffsA[3]
+
+    add     r11, r14, #XDELAYA-4
+    stmia   r11, { r4, r10 }        @ p->buf[XDELAYA-1] = r4
+                                    @ p->buf[XDELAYA] = r10
+
+    @ flags were set above, in the subs instruction
+    mvngt   r4, #0
+    movlt   r4, #1                 @ r4 := SIGN(r4) (see .c for SIGN macro)
+
+    cmp     r10, #0
+    mvngt   r10, #0
+    movlt   r10, #1                @ r10 := SIGN(r10) (see .c for SIGN macro)
+
+    add     r1, r14, #XADAPTCOEFFSA-4
+    stmia   r1, {r4, r10}           @ p->buf[XADAPTCOEFFSA-1] := r4
+                                    @ p->buf[XADAPTCOEFFSA] := r10
+
+    @ NOTE: r0 now contains predictionA - don't overwrite.
+
+@ Predictor X, Filter B
+
+    add     r2, r12, #XfilterB
+    ldmia   r2, {r2, r11}           @ r2 := p->XfilterB
+                                    @ r11 := p->YfilterA
+
+    rsb     r2, r2, r2, lsl #5      @ r2 := r2 * 32 - r2 ( == r2*31)
+    sub     r10, r11, r2, asr #5    @ r10 (p->buf[XDELAYB]) := r11 - (r2 >> 5)
+
+    str     r11, [r12, #XfilterB]   @ p->XfilterB := r11 (p->YfilterA)
+
+    add     r11, r14, #XDELAYB-16   @ r11 := &p->buf[XDELAYB-4]
+
+    ldmia   r11, { r2 - r5 }        @ r2 := p->buf[XDELAYB-4]
+                                    @ r3 := p->buf[XDELAYB-3]
+                                    @ r4 := p->buf[XDELAYB-2]
+                                    @ r5 := p->buf[XDELAYB-1]
+
+    subs     r5, r10, r5             @ r5 := r10 - r5
+
+    add     r1, r12, #XcoeffsB
+    ldmia   r1, {r6,r7,r8,r9,r11}   @ r6 := p->XcoeffsB[0]
+                                    @ r7 := p->XcoeffsB[1]
+                                    @ r8 := p->XcoeffsB[2]
+                                    @ r9 := p->XcoeffsB[3]
+                                    @ r11 := p->XcoeffsB[4]
+
+    mul     r1, r10, r6             @ r1 := p->buf[XDELAYB] * p->XcoeffsB[0]
+    mla     r1, r5, r7, r1          @ r1 += p->buf[XDELAYB-1] * p->XcoeffsB[1]
+    mla     r1, r4, r8, r1          @ r1 += p->buf[XDELAYB-2] * p->XcoeffsB[2]
+    mla     r1, r3, r9, r1          @ r1 += p->buf[XDELAYB-3] * p->XcoeffsB[3]
+    mla     r1, r2, r11, r1         @ r1 += p->buf[XDELAYB-4] * p->XcoeffsB[4]
+
+    add     r2, r14, #XDELAYB-4     @ r2 := &p->buf[XDELAYB-1]
+    stmia   r2, { r5, r10 }         @ p->buf[XDELAYB-1] = r5
+                                    @ p->buf[XDELAYB] = r10
+
+    @ flags were set above, in the subs instruction
+    mvngt   r5, #0
+    movlt   r5, #1                 @ r5 := SIGN(r5) (see .c for SIGN macro)
+
+    cmp     r10, #0
+    mvngt   r10, #0
+    movlt   r10, #1                @ r10 := SIGN(r10) (see .c for SIGN macro)
+
+    add     r2, r14, #XADAPTCOEFFSB-4
+    stmia   r2, {r5, r10}           @ p->buf[XADAPTCOEFFSB-1] := r5
+                                    @ p->buf[XADAPTCOEFFSB] := r10
+
+    @ r0 still contains predictionA
+    @ r1 contains predictionB
+
+    @ Finish Predictor X
+
+    ldr     r2, [sp, #4]            @ r2 := decoded1
+    add     r0, r0, r1, asr #1      @ r0 := r0 + (r1 >> 1)
+    ldr     r3, [r2]                @ r3 := *decoded1
+    add     r1, r3, r0, asr #10     @ r1 := r3 + (r0 >> 10)
+    str     r1, [r12, #XlastA]      @ p->XlastA := r1
+
+    ldr     r4, [r12, #XfilterA]    @ r4 := p->XfilterA
+    rsb     r4, r4, r4, lsl #5      @ r4 := r4 * 32 - r4 ( == r4*31)
+    add     r1, r1, r4, asr #5      @ r1 := r1 + (r4 >> 5)
+    str     r1, [r12, #XfilterA]    @ p->XfilterA := r1
+
+    @ r1 contains p->XfilterA
+    @ r2 contains decoded1
+    @ r3 contains *decoded1
+
+    @ r6, r7, r8, r9, r11 contain p->XcoeffsB[0..4]
+    @ r5, r10 contain p->buf[XADAPTCOEFFSB-1] and p->buf[XADAPTCOEFFSB]
+
+    cmp     r3, #0
+    stmia   r2!, {r1}               @ *(decoded1++) := r1  (p->XfilterA)
+    str     r2, [sp, #4]            @ save decoded1
+    beq     2f
+
+    add     r1, r14, #XADAPTCOEFFSB-16
+    ldmia   r1, { r2, r3, r4 }      @ r2 := p->buf[XADAPTCOEFFSB-4]
+                                    @ r3 := p->buf[XADAPTCOEFFSB-3]
+                                    @ r4 := p->buf[XADAPTCOEFFSB-2]
+    blt     1f
+
+    @ *decoded1 > 0
+
+    sub     r6, r6, r10       @ r6 := p->XcoeffsB[0] - p->buf[XADAPTCOEFFSB]
+    sub     r7, r7, r5        @ r7 := p->XcoeffsB[1] - p->buf[XADAPTCOEFFSB-1]
+    sub     r8, r8, r4        @ r8 := p->XcoeffsB[2] - p->buf[XADAPTCOEFFSB-2]
+    sub     r9, r9, r3        @ r9 := p->XcoeffsB[3] - p->buf[XADAPTCOEFFSB-3]
+    sub     r11, r11, r2            @ r11 := p->XcoeffsB[4] - p->buf[XADAPTCOEFFSB-4]
+
+    add     r0, r12, #XcoeffsB      
+    stmia   r0, {r6,r7,r8,r9,r11}   @ Save p->XcoeffsB[]
+
+    add     r1, r12, #XcoeffsA
+    ldmia   r1, { r2-r5 }           @ r2 := p->XcoeffsA[0]
+                                    @ r3 := p->XcoeffsA[1]
+                                    @ r4 := p->XcoeffsA[2]
+                                    @ r5 := p->XcoeffsA[3]
+
+    add     r0, r14, #XADAPTCOEFFSA-12
+    ldmia   r0, { r6-r9}            @ r6 := p->buf[XADAPTCOEFFSA-3]
+                                    @ r7 := p->buf[XADAPTCOEFFSA-2]
+                                    @ r8 := p->buf[XADAPTCOEFFSA-1]
+                                    @ r9 := p->buf[XADAPTCOEFFSA]
+
+    sub     r2, r2, r9        @ r2 := p->XcoeffsA[0] - p->buf[XADAPTCOEFFSA]
+    sub     r3, r3, r8        @ r3 := p->XcoeffsA[1] - p->buf[XADAPTCOEFFSA-1]
+    sub     r4, r4, r7        @ r4 := p->XcoeffsA[2] - p->buf[XADAPTCOEFFSA-2]
+    sub     r5, r5, r6        @ r5 := p->XcoeffsA[3] - p->buf[XADAPTCOEFFSA-3]
+    
+    stmia   r1, {r2-r5}             @ Save p->XcoeffsA
+    b       2f
+
+
+1:  @ *decoded1 < 0
+
+    add     r6, r6, r10       @ r6 := p->XcoeffsB[0] + p->buf[XADAPTCOEFFSB]
+    add     r7, r7, r5        @ r7 := p->XcoeffsB[1] + p->buf[XADAPTCOEFFSB-1]
+    add     r8, r8, r4        @ r8 := p->XcoeffsB[2] + p->buf[XADAPTCOEFFSB-2]
+    add     r9, r9, r3        @ r9 := p->XcoeffsB[3] + p->buf[XADAPTCOEFFSB-3]
+    add     r11, r11, r2      @ r11 := p->XcoeffsB[4] + p->buf[XADAPTCOEFFSB-4]
+
+    add     r0, r12, #XcoeffsB      
+    stmia   r0, {r6,r7,r8,r9,r11}   @ Save p->XcoeffsB[]
+
+    add     r1, r12, #XcoeffsA
+    ldmia   r1, { r2-r5 }           @ r2 := p->XcoeffsA[0]
+                                    @ r3 := p->XcoeffsA[1]
+                                    @ r4 := p->XcoeffsA[2]
+                                    @ r5 := p->XcoeffsA[3]
+
+    add     r0, r14, #XADAPTCOEFFSA-12
+    ldmia   r0, { r6-r9}            @ r6 := p->buf[XADAPTCOEFFSA-3]
+                                    @ r7 := p->buf[XADAPTCOEFFSA-2]
+                                    @ r8 := p->buf[XADAPTCOEFFSA-1]
+                                    @ r9 := p->buf[XADAPTCOEFFSA]
+
+    add     r2, r2, r9        @ r2 := p->XcoeffsA[0] + p->buf[XADAPTCOEFFSA]
+    add     r3, r3, r8        @ r3 := p->XcoeffsA[1] + p->buf[XADAPTCOEFFSA-1]
+    add     r4, r4, r7        @ r4 := p->XcoeffsA[2] + p->buf[XADAPTCOEFFSA-2]
+    add     r5, r5, r6        @ r5 := p->XcoeffsA[3] + p->buf[XADAPTCOEFFSA-3]
+    
+    stmia   r1, {r2-r5}             @ Save p->XcoeffsA
+
+2:
+    
+@@@@@@@@@@@@@@@@@@@@@@@@@@@ COMMON
+
+    add     r14, r14, #4                @ p->buf++
+
+    add     r11, r12, #historybuffer    @ r11 := &p->historybuffer[0]
+
+    sub     r10, r14, #HISTORY_SIZE*4   @ r10 := p->buf - HISTORY_SIZE
+
+    cmp     r10, r11
+    bne     endofloop
+
+    @ The history buffer is full, we need to do a memmove:
+
+    @ dest = r11 (p->historybuffer)
+    @ src = r14 (p->buf)
+    @ n = 200
+
+    ldmia   r14!, {r0-r9}    @ 40 bytes
+    stmia   r11!, {r0-r9}
+    ldmia   r14!, {r0-r9}    @ 40 bytes
+    stmia   r11!, {r0-r9}
+    ldmia   r14!, {r0-r9}    @ 40 bytes
+    stmia   r11!, {r0-r9}
+    ldmia   r14!, {r0-r9}    @ 40 bytes
+    stmia   r11!, {r0-r9}
+    ldmia   r14!, {r0-r9}    @ 40 bytes
+    stmia   r11!, {r0-r9}
+
+    add     r14, r12, #historybuffer    @ p->buf = &p->historybuffer[0]
+
+
+endofloop:
+@ Check loop count
+    ldr     r0, [sp, #8]
+    subs    r0, r0, #1
+    strne   r0, [sp, #8]
+    bne     loop
+
+done:
+    str     r14, [r12]              @ Save value of p->buf
+    add     sp, sp, #12             @ Don't bother restoring r1-r3 
+    ldmia   sp!, {r4-r11, pc}
diff --git a/apps/codecs/demac/libdemac/predictor.c b/apps/codecs/demac/libdemac/predictor.c
index a7210bf014..90f24e416b 100644
--- a/apps/codecs/demac/libdemac/predictor.c
+++ b/apps/codecs/demac/libdemac/predictor.c
@@ -74,6 +74,7 @@ void init_predictor_decoder(struct predictor_t* p)
 int predictor_decode_stereo(struct predictor_t* p, int32_t* decoded0, int32_t* decoded1, int count) ICODE_ATTR;
 #endif
 
+#ifndef CPU_ARM
 int predictor_decode_stereo(struct predictor_t* p, int32_t* decoded0, int32_t* decoded1, int count)
 {
     int32_t predictionA, predictionB;
@@ -208,6 +209,7 @@ int predictor_decode_stereo(struct predictor_t* p, int32_t* decoded0, int32_t* d
 
     return 0;
 }
+#endif
 
 int predictor_decode_mono(struct predictor_t* p, int32_t* decoded0, int count)
 {