/* * simple_idct_arm.S * Copyright (C) 2002 Frederic 'dilb' Boulay. * All Rights Reserved. * * Author: Frederic Boulay * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg 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 * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 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