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FFmpeg/libavcodec/armv4l/simple_idct_arm.S

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/*
* simple_idct_arm.S
* Copyright (C) 2002 Frederic 'dilb' Boulay.
* All Rights Reserved.
*
* Author: Frederic Boulay <dilb@handhelds.org>
*
* You can redistribute this file and/or modify
* it under the terms of the GNU General Public License (version 2)
* as published by the Free Software Foundation.
*
* This file 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 library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*
* The function defined in this file, is derived from the simple_idct function
* from the libavcodec library part of the ffmpeg project.
*/
/* useful constants for the algorithm, they are save in __constant_ptr__ at */
/* the end of the source code.*/
#define W1 22725
#define W2 21407
#define W3 19266
#define W4 16383
#define W5 12873
#define W6 8867
#define W7 4520
#define MASK_MSHW 0xFFFF0000
/* offsets of the constants in the vector */
#define offW1 0
#define offW2 4
#define offW3 8
#define offW4 12
#define offW5 16
#define offW6 20
#define offW7 24
#define offMASK_MSHW 28
#define ROW_SHIFT 11
#define ROW_SHIFT2MSHW (16-11)
#define COL_SHIFT 20
#define ROW_SHIFTED_1 1024 /* 1<< (ROW_SHIFT-1) */
#define COL_SHIFTED_1 524288 /* 1<< (COL_SHIFT-1) */
.text
.align
.global simple_idct_ARM
simple_idct_ARM:
@@ void simple_idct_ARM(int16_t *block)
@@ save stack for reg needed (take all of them),
@@ R0-R3 are scratch regs, so no need to save them, but R0 contains the pointer to block
@@ so it must not be overwritten, if it is not saved!!
@@ R12 is another scratch register, so it should not be saved too
@@ save all registers
stmfd sp!, {r4-r11, r14} @ R14 is also called LR
@@ at this point, R0=block, other registers are free.
add r14, r0, #112 @ R14=&block[8*7], better start from the last row, and decrease the value until row=0, i.e. R12=block.
add r12, pc, #(__constant_ptr__-.-8) @ R12=__constant_ptr__, the vector containing the constants, probably not necessary to reserve a register for it
@@ add 2 temporary variables in the stack: R0 and R14
sub sp, sp, #8 @ allow 2 local variables
str r0, [sp, #0] @ save block in sp[0]
@@ stack status
@@ sp+4 free
@@ sp+0 R0 (block)
@@ at this point, R0=block, R14=&block[56], R12=__const_ptr_, R1-R11 free
__row_loop:
@@ read the row and check if it is null, almost null, or not, according to strongarm specs, it is not necessary to optimise ldr accesses (i.e. split 32bits in 2 16bits words), at least it gives more usable registers :)
ldr r1, [r14, #0] @ R1=(int32)(R12)[0]=ROWr32[0] (relative row cast to a 32b pointer)
ldr r2, [r14, #4] @ R2=(int32)(R12)[1]=ROWr32[1]
ldr r3, [r14, #8] @ R3=ROWr32[2]
ldr r4, [r14, #12] @ R4=ROWr32[3]
@@ check if the words are null, if all of them are null, then proceed with next row (branch __end_row_loop),
@@ if ROWr16[0] is the only one not null, then proceed with this special case (branch __almost_empty_row)
@@ else follow the complete algorithm.
@@ at this point, R0=block, R14=&block[n], R12=__const_ptr_, R1=ROWr32[0], R2=ROWr32[1],
@@ R3=ROWr32[2], R4=ROWr32[3], R5-R11 free
orr r5, r4, r3 @ R5=R4 | R3
orr r5, r5, r2 @ R5=R4 | R3 | R2
orrs r6, r5, r1 @ Test R5 | R1 (the aim is to check if everything is null)
beq __end_row_loop
mov r7, r1, asr #16 @ R7=R1>>16=ROWr16[1] (evaluate it now, as it could be useful later)
ldrsh r6, [r14, #0] @ R6=ROWr16[0]
orrs r5, r5, r7 @ R5=R4 | R3 | R2 | R7
beq __almost_empty_row
__b_evaluation:
@@ at this point, R0=block (temp), R1(free), R2=ROWr32[1], R3=ROWr32[2], R4=ROWr32[3],
@@ R5=(temp), R6=ROWr16[0], R7=ROWr16[1], R8-R11 free,
@@ R12=__const_ptr_, R14=&block[n]
@@ to save some registers/calls, proceed with b0-b3 first, followed by a0-a3
@@ MUL16(b0, W1, row[1]);
@@ MUL16(b1, W3, row[1]);
@@ MUL16(b2, W5, row[1]);
@@ MUL16(b3, W7, row[1]);
@@ MAC16(b0, W3, row[3]);
@@ MAC16(b1, -W7, row[3]);
@@ MAC16(b2, -W1, row[3]);
@@ MAC16(b3, -W5, row[3]);
ldr r8, [r12, #offW1] @ R8=W1
mov r2, r2, asr #16 @ R2=ROWr16[3]
mul r0, r8, r7 @ R0=W1*ROWr16[1]=b0 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
ldr r9, [r12, #offW3] @ R9=W3
ldr r10, [r12, #offW5] @ R10=W5
mul r1, r9, r7 @ R1=W3*ROWr16[1]=b1 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
ldr r11, [r12, #offW7] @ R11=W7
mul r5, r10, r7 @ R5=W5*ROWr16[1]=b2 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
mul r7, r11, r7 @ R7=W7*ROWr16[1]=b3 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
teq r2, #0 @ if null avoid muls
mlane r0, r9, r2, r0 @ R0+=W3*ROWr16[3]=b0 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
rsbne r2, r2, #0 @ R2=-ROWr16[3]
mlane r1, r11, r2, r1 @ R1-=W7*ROWr16[3]=b1 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
mlane r5, r8, r2, r5 @ R5-=W1*ROWr16[3]=b2 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
mlane r7, r10, r2, r7 @ R7-=W5*ROWr16[3]=b3 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
@@ at this point, R0=b0, R1=b1, R2 (free), R3=ROWr32[2], R4=ROWr32[3],
@@ R5=b2, R6=ROWr16[0], R7=b3, R8=W1, R9=W3, R10=W5, R11=W7,
@@ R12=__const_ptr_, R14=&block[n]
@@ temp = ((uint32_t*)row)[2] | ((uint32_t*)row)[3];
@@ if (temp != 0) {}
orrs r2, r3, r4 @ R2=ROWr32[2] | ROWr32[3]
beq __end_b_evaluation
@@ at this point, R0=b0, R1=b1, R2 (free), R3=ROWr32[2], R4=ROWr32[3],
@@ R5=b2, R6=ROWr16[0], R7=b3, R8=W1, R9=W3, R10=W5, R11=W7,
@@ R12=__const_ptr_, R14=&block[n]
@@ MAC16(b0, W5, row[5]);
@@ MAC16(b2, W7, row[5]);
@@ MAC16(b3, W3, row[5]);
@@ MAC16(b1, -W1, row[5]);
@@ MAC16(b0, W7, row[7]);
@@ MAC16(b2, W3, row[7]);
@@ MAC16(b3, -W1, row[7]);
@@ MAC16(b1, -W5, row[7]);
mov r3, r3, asr #16 @ R3=ROWr16[5]
teq r3, #0 @ if null avoid muls
mlane r0, r10, r3, r0 @ R0+=W5*ROWr16[5]=b0
mov r4, r4, asr #16 @ R4=ROWr16[7]
mlane r5, r11, r3, r5 @ R5+=W7*ROWr16[5]=b2
mlane r7, r9, r3, r7 @ R7+=W3*ROWr16[5]=b3
rsbne r3, r3, #0 @ R3=-ROWr16[5]
mlane r1, r8, r3, r1 @ R7-=W1*ROWr16[5]=b1
@@ R3 is free now
teq r4, #0 @ if null avoid muls
mlane r0, r11, r4, r0 @ R0+=W7*ROWr16[7]=b0
mlane r5, r9, r4, r5 @ R5+=W3*ROWr16[7]=b2
rsbne r4, r4, #0 @ R4=-ROWr16[7]
mlane r7, r8, r4, r7 @ R7-=W1*ROWr16[7]=b3
mlane r1, r10, r4, r1 @ R1-=W5*ROWr16[7]=b1
@@ R4 is free now
__end_b_evaluation:
@@ at this point, R0=b0, R1=b1, R2=ROWr32[2] | ROWr32[3] (tmp), R3 (free), R4 (free),
@@ R5=b2, R6=ROWr16[0], R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
__a_evaluation:
@@ a0 = (W4 * row[0]) + (1 << (ROW_SHIFT - 1));
@@ a1 = a0 + W6 * row[2];
@@ a2 = a0 - W6 * row[2];
@@ a3 = a0 - W2 * row[2];
@@ a0 = a0 + W2 * row[2];
ldr r9, [r12, #offW4] @ R9=W4
mul r6, r9, r6 @ R6=W4*ROWr16[0]
ldr r10, [r12, #offW6] @ R10=W6
ldrsh r4, [r14, #4] @ R4=ROWr16[2] (a3 not defined yet)
add r6, r6, #ROW_SHIFTED_1 @ R6=W4*ROWr16[0] + 1<<(ROW_SHIFT-1) (a0)
mul r11, r10, r4 @ R11=W6*ROWr16[2]
ldr r8, [r12, #offW2] @ R8=W2
sub r3, r6, r11 @ R3=a0-W6*ROWr16[2] (a2)
@@ temp = ((uint32_t*)row)[2] | ((uint32_t*)row)[3];
@@ if (temp != 0) {}
teq r2, #0
beq __end_bef_a_evaluation
add r2, r6, r11 @ R2=a0+W6*ROWr16[2] (a1)
mul r11, r8, r4 @ R11=W2*ROWr16[2]
sub r4, r6, r11 @ R4=a0-W2*ROWr16[2] (a3)
add r6, r6, r11 @ R6=a0+W2*ROWr16[2] (a0)
@@ at this point, R0=b0, R1=b1, R2=a1, R3=a2, R4=a3,
@@ R5=b2, R6=a0, R7=b3, R8=W2, R9=W4, R10=W6, R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
@@ a0 += W4*row[4]
@@ a1 -= W4*row[4]
@@ a2 -= W4*row[4]
@@ a3 += W4*row[4]
ldrsh r11, [r14, #8] @ R11=ROWr16[4]
teq r11, #0 @ if null avoid muls
mulne r11, r9, r11 @ R11=W4*ROWr16[4]
@@ R9 is free now
ldrsh r9, [r14, #12] @ R9=ROWr16[6]
addne r6, r6, r11 @ R6+=W4*ROWr16[4] (a0)
subne r2, r2, r11 @ R2-=W4*ROWr16[4] (a1)
subne r3, r3, r11 @ R3-=W4*ROWr16[4] (a2)
addne r4, r4, r11 @ R4+=W4*ROWr16[4] (a3)
@@ W6 alone is no more useful, save W2*ROWr16[6] in it instead
teq r9, #0 @ if null avoid muls
mulne r11, r10, r9 @ R11=W6*ROWr16[6]
addne r6, r6, r11 @ R6+=W6*ROWr16[6] (a0)
mulne r10, r8, r9 @ R10=W2*ROWr16[6]
@@ a0 += W6*row[6];
@@ a3 -= W6*row[6];
@@ a1 -= W2*row[6];
@@ a2 += W2*row[6];
subne r4, r4, r11 @ R4-=W6*ROWr16[6] (a3)
subne r2, r2, r10 @ R2-=W2*ROWr16[6] (a1)
addne r3, r3, r10 @ R3+=W2*ROWr16[6] (a2)
__end_a_evaluation:
@@ at this point, R0=b0, R1=b1, R2=a1, R3=a2, R4=a3,
@@ R5=b2, R6=a0, R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
@@ row[0] = (a0 + b0) >> ROW_SHIFT;
@@ row[1] = (a1 + b1) >> ROW_SHIFT;
@@ row[2] = (a2 + b2) >> ROW_SHIFT;
@@ row[3] = (a3 + b3) >> ROW_SHIFT;
@@ row[4] = (a3 - b3) >> ROW_SHIFT;
@@ row[5] = (a2 - b2) >> ROW_SHIFT;
@@ row[6] = (a1 - b1) >> ROW_SHIFT;
@@ row[7] = (a0 - b0) >> ROW_SHIFT;
add r8, r6, r0 @ R8=a0+b0
add r9, r2, r1 @ R9=a1+b1
@@ put 2 16 bits half-words in a 32bits word
@@ ROWr32[0]=ROWr16[0] | (ROWr16[1]<<16) (only Little Endian compliant then!!!)
ldr r10, [r12, #offMASK_MSHW] @ R10=0xFFFF0000
and r9, r10, r9, lsl #ROW_SHIFT2MSHW @ R9=0xFFFF0000 & ((a1+b1)<<5)
mvn r11, r10 @ R11= NOT R10= 0x0000FFFF
and r8, r11, r8, asr #ROW_SHIFT @ R8=0x0000FFFF & ((a0+b0)>>11)
orr r8, r8, r9
str r8, [r14, #0]
add r8, r3, r5 @ R8=a2+b2
add r9, r4, r7 @ R9=a3+b3
and r9, r10, r9, lsl #ROW_SHIFT2MSHW @ R9=0xFFFF0000 & ((a3+b3)<<5)
and r8, r11, r8, asr #ROW_SHIFT @ R8=0x0000FFFF & ((a2+b2)>>11)
orr r8, r8, r9
str r8, [r14, #4]
sub r8, r4, r7 @ R8=a3-b3
sub r9, r3, r5 @ R9=a2-b2
and r9, r10, r9, lsl #ROW_SHIFT2MSHW @ R9=0xFFFF0000 & ((a2-b2)<<5)
and r8, r11, r8, asr #ROW_SHIFT @ R8=0x0000FFFF & ((a3-b3)>>11)
orr r8, r8, r9
str r8, [r14, #8]
sub r8, r2, r1 @ R8=a1-b1
sub r9, r6, r0 @ R9=a0-b0
and r9, r10, r9, lsl #ROW_SHIFT2MSHW @ R9=0xFFFF0000 & ((a0-b0)<<5)
and r8, r11, r8, asr #ROW_SHIFT @ R8=0x0000FFFF & ((a1-b1)>>11)
orr r8, r8, r9
str r8, [r14, #12]
bal __end_row_loop
__almost_empty_row:
@@ the row was empty, except ROWr16[0], now, management of this special case
@@ at this point, R0=block, R14=&block[n], R12=__const_ptr_, R1=ROWr32[0], R2=ROWr32[1],
@@ R3=ROWr32[2], R4=ROWr32[3], R5=(temp), R6=ROWr16[0], R7=ROWr16[1],
@@ R8=0xFFFF (temp), R9-R11 free
mov r8, #0x10000 @ R8=0xFFFF (2 steps needed!) it saves a ldr call (because of delay run).
sub r8, r8, #1 @ R8 is now ready.
and r5, r8, r6, lsl #3 @ R5=R8 & (R6<<3)= (ROWr16[0]<<3) & 0xFFFF
orr r5, r5, r5, lsl #16 @ R5=R5 | (R5<<16)
str r5, [r14, #0] @ R14[0]=ROWr32[0]=R5
str r5, [r14, #4] @ R14[4]=ROWr32[1]=R5
str r5, [r14, #8] @ R14[8]=ROWr32[2]=R5
str r5, [r14, #12] @ R14[12]=ROWr32[3]=R5
__end_row_loop:
@@ at this point, R0-R11 (free)
@@ R12=__const_ptr_, R14=&block[n]
ldr r0, [sp, #0] @ R0=block
teq r0, r14 @ compare current &block[8*n] to block, when block is reached, the loop is finished.
sub r14, r14, #16
bne __row_loop
@@ at this point, R0=block, R1-R11 (free)
@@ R12=__const_ptr_, R14=&block[n]
add r14, r0, #14 @ R14=&block[7], better start from the last col, and decrease the value until col=0, i.e. R14=block.
__col_loop:
__b_evaluation2:
@@ at this point, R0=block (temp), R1-R11 (free)
@@ R12=__const_ptr_, R14=&block[n]
@@ proceed with b0-b3 first, followed by a0-a3
@@ MUL16(b0, W1, col[8x1]);
@@ MUL16(b1, W3, col[8x1]);
@@ MUL16(b2, W5, col[8x1]);
@@ MUL16(b3, W7, col[8x1]);
@@ MAC16(b0, W3, col[8x3]);
@@ MAC16(b1, -W7, col[8x3]);
@@ MAC16(b2, -W1, col[8x3]);
@@ MAC16(b3, -W5, col[8x3]);
ldr r8, [r12, #offW1] @ R8=W1
ldrsh r7, [r14, #16]
mul r0, r8, r7 @ R0=W1*ROWr16[1]=b0 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
ldr r9, [r12, #offW3] @ R9=W3
ldr r10, [r12, #offW5] @ R10=W5
mul r1, r9, r7 @ R1=W3*ROWr16[1]=b1 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
ldr r11, [r12, #offW7] @ R11=W7
mul r5, r10, r7 @ R5=W5*ROWr16[1]=b2 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
ldrsh r2, [r14, #48]
mul r7, r11, r7 @ R7=W7*ROWr16[1]=b3 (ROWr16[1] must be the second arg, to have the possibility to save 1 cycle)
teq r2, #0 @ if 0, then avoid muls
mlane r0, r9, r2, r0 @ R0+=W3*ROWr16[3]=b0 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
rsbne r2, r2, #0 @ R2=-ROWr16[3]
mlane r1, r11, r2, r1 @ R1-=W7*ROWr16[3]=b1 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
mlane r5, r8, r2, r5 @ R5-=W1*ROWr16[3]=b2 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
mlane r7, r10, r2, r7 @ R7-=W5*ROWr16[3]=b3 (ROWr16[3] must be the second arg, to have the possibility to save 1 cycle)
@@ at this point, R0=b0, R1=b1, R2 (free), R3 (free), R4 (free),
@@ R5=b2, R6 (free), R7=b3, R8=W1, R9=W3, R10=W5, R11=W7,
@@ R12=__const_ptr_, R14=&block[n]
@@ MAC16(b0, W5, col[5x8]);
@@ MAC16(b2, W7, col[5x8]);
@@ MAC16(b3, W3, col[5x8]);
@@ MAC16(b1, -W1, col[5x8]);
@@ MAC16(b0, W7, col[7x8]);
@@ MAC16(b2, W3, col[7x8]);
@@ MAC16(b3, -W1, col[7x8]);
@@ MAC16(b1, -W5, col[7x8]);
ldrsh r3, [r14, #80] @ R3=COLr16[5x8]
teq r3, #0 @ if 0 then avoid muls
mlane r0, r10, r3, r0 @ R0+=W5*ROWr16[5x8]=b0
mlane r5, r11, r3, r5 @ R5+=W7*ROWr16[5x8]=b2
mlane r7, r9, r3, r7 @ R7+=W3*ROWr16[5x8]=b3
rsbne r3, r3, #0 @ R3=-ROWr16[5x8]
ldrsh r4, [r14, #112] @ R4=COLr16[7x8]
mlane r1, r8, r3, r1 @ R7-=W1*ROWr16[5x8]=b1
@@ R3 is free now
teq r4, #0 @ if 0 then avoid muls
mlane r0, r11, r4, r0 @ R0+=W7*ROWr16[7x8]=b0
mlane r5, r9, r4, r5 @ R5+=W3*ROWr16[7x8]=b2
rsbne r4, r4, #0 @ R4=-ROWr16[7x8]
mlane r7, r8, r4, r7 @ R7-=W1*ROWr16[7x8]=b3
mlane r1, r10, r4, r1 @ R1-=W5*ROWr16[7x8]=b1
@@ R4 is free now
__end_b_evaluation2:
@@ at this point, R0=b0, R1=b1, R2 (free), R3 (free), R4 (free),
@@ R5=b2, R6 (free), R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
__a_evaluation2:
@@ a0 = (W4 * col[8x0]) + (1 << (COL_SHIFT - 1));
@@ a1 = a0 + W6 * row[2];
@@ a2 = a0 - W6 * row[2];
@@ a3 = a0 - W2 * row[2];
@@ a0 = a0 + W2 * row[2];
ldrsh r6, [r14, #0]
ldr r9, [r12, #offW4] @ R9=W4
mul r6, r9, r6 @ R6=W4*ROWr16[0]
ldr r10, [r12, #offW6] @ R10=W6
ldrsh r4, [r14, #32] @ R4=ROWr16[2] (a3 not defined yet)
add r6, r6, #COL_SHIFTED_1 @ R6=W4*ROWr16[0] + 1<<(COL_SHIFT-1) (a0)
mul r11, r10, r4 @ R11=W6*ROWr16[2]
ldr r8, [r12, #offW2] @ R8=W2
add r2, r6, r11 @ R2=a0+W6*ROWr16[2] (a1)
sub r3, r6, r11 @ R3=a0-W6*ROWr16[2] (a2)
mul r11, r8, r4 @ R11=W2*ROWr16[2]
sub r4, r6, r11 @ R4=a0-W2*ROWr16[2] (a3)
add r6, r6, r11 @ R6=a0+W2*ROWr16[2] (a0)
@@ at this point, R0=b0, R1=b1, R2=a1, R3=a2, R4=a3,
@@ R5=b2, R6=a0, R7=b3, R8=W2, R9=W4, R10=W6, R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
@@ a0 += W4*row[4]
@@ a1 -= W4*row[4]
@@ a2 -= W4*row[4]
@@ a3 += W4*row[4]
ldrsh r11, [r14, #64] @ R11=ROWr16[4]
teq r11, #0 @ if null avoid muls
mulne r11, r9, r11 @ R11=W4*ROWr16[4]
@@ R9 is free now
addne r6, r6, r11 @ R6+=W4*ROWr16[4] (a0)
subne r2, r2, r11 @ R2-=W4*ROWr16[4] (a1)
subne r3, r3, r11 @ R3-=W4*ROWr16[4] (a2)
ldrsh r9, [r14, #96] @ R9=ROWr16[6]
addne r4, r4, r11 @ R4+=W4*ROWr16[4] (a3)
@@ W6 alone is no more useful, save W2*ROWr16[6] in it instead
teq r9, #0 @ if null avoid muls
mulne r11, r10, r9 @ R11=W6*ROWr16[6]
addne r6, r6, r11 @ R6+=W6*ROWr16[6] (a0)
mulne r10, r8, r9 @ R10=W2*ROWr16[6]
@@ a0 += W6*row[6];
@@ a3 -= W6*row[6];
@@ a1 -= W2*row[6];
@@ a2 += W2*row[6];
subne r4, r4, r11 @ R4-=W6*ROWr16[6] (a3)
subne r2, r2, r10 @ R2-=W2*ROWr16[6] (a1)
addne r3, r3, r10 @ R3+=W2*ROWr16[6] (a2)
__end_a_evaluation2:
@@ at this point, R0=b0, R1=b1, R2=a1, R3=a2, R4=a3,
@@ R5=b2, R6=a0, R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
@@ R12=__const_ptr_, R14=&block[n]
@@ col[0 ] = ((a0 + b0) >> COL_SHIFT);
@@ col[8 ] = ((a1 + b1) >> COL_SHIFT);
@@ col[16] = ((a2 + b2) >> COL_SHIFT);
@@ col[24] = ((a3 + b3) >> COL_SHIFT);
@@ col[32] = ((a3 - b3) >> COL_SHIFT);
@@ col[40] = ((a2 - b2) >> COL_SHIFT);
@@ col[48] = ((a1 - b1) >> COL_SHIFT);
@@ col[56] = ((a0 - b0) >> COL_SHIFT);
@@@@@ no optimisation here @@@@@
add r8, r6, r0 @ R8=a0+b0
add r9, r2, r1 @ R9=a1+b1
mov r8, r8, asr #COL_SHIFT
mov r9, r9, asr #COL_SHIFT
strh r8, [r14, #0]
strh r9, [r14, #16]
add r8, r3, r5 @ R8=a2+b2
add r9, r4, r7 @ R9=a3+b3
mov r8, r8, asr #COL_SHIFT
mov r9, r9, asr #COL_SHIFT
strh r8, [r14, #32]
strh r9, [r14, #48]
sub r8, r4, r7 @ R8=a3-b3
sub r9, r3, r5 @ R9=a2-b2
mov r8, r8, asr #COL_SHIFT
mov r9, r9, asr #COL_SHIFT
strh r8, [r14, #64]
strh r9, [r14, #80]
sub r8, r2, r1 @ R8=a1-b1
sub r9, r6, r0 @ R9=a0-b0
mov r8, r8, asr #COL_SHIFT
mov r9, r9, asr #COL_SHIFT
strh r8, [r14, #96]
strh r9, [r14, #112]
__end_col_loop:
@@ at this point, R0-R11 (free)
@@ R12=__const_ptr_, R14=&block[n]
ldr r0, [sp, #0] @ R0=block
teq r0, r14 @ compare current &block[n] to block, when block is reached, the loop is finished.
sub r14, r14, #2
bne __col_loop
__end_simple_idct_ARM:
@@ restore registers to previous status!
add sp, sp, #8 @@ the local variables!
ldmfd sp!, {r4-r11, r15} @@ update PC with LR content.
@@ kind of sub-function, here not to overload the common case.
__end_bef_a_evaluation:
add r2, r6, r11 @ R2=a0+W6*ROWr16[2] (a1)
mul r11, r8, r4 @ R11=W2*ROWr16[2]
sub r4, r6, r11 @ R4=a0-W2*ROWr16[2] (a3)
add r6, r6, r11 @ R6=a0+W2*ROWr16[2] (a0)
bal __end_a_evaluation
__constant_ptr__: @@ see #defines at the beginning of the source code for values.
.align
.word W1
.word W2
.word W3
.word W4
.word W5
.word W6
.word W7
.word MASK_MSHW
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