以下MIPS过程旨在读取和写入内存中加载的BMP图像中的像素。
.eqv BMP_FILE_SIZE 90122
.eqv BYTES_PER_ROW 1800
put_pixel:
#description:
# sets the color of specified pixel
#arguments:
# $a0 - x coordinate
# $a1 - y coordinate - (0,0) - bottom left corner
# $a2 - 0RGB - pixel color
#return value: none
sub $sp, $sp, 4 #push $ra to the stack
sw $ra,4($sp)
la $t1, image + 10 #adress of file offset to pixel array
lw $t2, ($t1) #file offset to pixel array in $t2
la $t1, image #adress of bitmap
add $t2, $t1, $t2 #adress of pixel array in $t2
#pixel address calculation
mul $t1, $a1, BYTES_PER_ROW #t1= y*BYTES_PER_ROW
move $t3, $a0
sll $a0, $a0, 1
add $t3, $t3, $a0 #$t3= 3*x
add $t1, $t1, $t3 #$t1 = 3x + y*BYTES_PER_ROW
add $t2, $t2, $t1 #pixel address
#set new color
sb $a2,($t2) #store B
srl $a2,$a2,8
sb $a2,1($t2) #store G
srl $a2,$a2,8
sb $a2,2($t2) #store R
lw $ra, 4($sp) #restore (pop) $ra
add $sp, $sp, 4
jr $ra
#
get_pixel:
#description:
# returns color of specified pixel
#arguments:
# $a0 - x coordinate
# $a1 - y coordinate - (0,0) - bottom left corner
#return value:
# $v0 - 0RGB - pixel color
sub $sp, $sp, 4 #push $ra to the stack
sw $ra,4($sp)
la $t1, image + 10 #adress of file offset to pixel array
lw $t2, ($t1) #file offset to pixel array in $t2
la $t1, image #adress of bitmap
add $t2, $t1, $t2 #adress of pixel array in $t2
#pixel address calculation
mul $t1, $a1, BYTES_PER_ROW #t1= y*BYTES_PER_ROW
move $t3, $a0
sll $a0, $a0, 1
add $t3, $t3, $a0 #$t3= 3*x
add $t1, $t1, $t3 #$t1 = 3x + y*BYTES_PER_ROW
add $t2, $t2, $t1 #pixel address
#get color
lbu $v0,($t2) #load B
lbu $t1,1($t2) #load G
sll $t1,$t1,8
or $v0, $v0, $t1
lbu $t1,2($t2) #load R
sll $t1,$t1,16
or $v0, $v0, $t1
lw $ra, 4($sp) #restore (pop) $ra
add $sp, $sp, 4
jr $ra
这些功能似乎效率不高。
如何在MIPS中提高像素读取和写入功能的效率？