【发布时间】：2015-12-06 21:31:35
【问题描述】：
我在优化 Eratosthenes 筛的代码方面取得了一些进展，但我需要进一步提高指令数和数据缓存命中率。任何帮助表示赞赏。
.data # the data segment to store global data
space: .asciiz " " # whitespace to separate prime numbers
.text # the text segment to store instructions
.globl main # define main to be a global label
main: li $s0, 0x00000000 # initialize $s0 with zeros
nor $s1, $s0, $s0 # saves one ALU count over using li $s1, 0x11111111
li $t9, 200 # find prime numbers from 2 to $t9
add $s2, $sp, 0 # backup bottom of stack address in $s2
li $t0, 2 # set counter variable to 2
init: sw $s1, ($sp) # write ones to the stackpointer's address
add $t0, $t0, 1 # increment counter variable
sub $sp, $sp, 4 # subtract 4 bytes from stackpointer (push)
bne $t0, $t9, init # take loop if $t0 != $t9, changed ble to bne
addi $t8, $t0, 15 # approximate square root of 200
li $t0, 1 # reset counter variable to 1
outer: add $t0, $t0, 2 # increment counter variable (start at 2)
mul $t1, $t0, $t0 # squaring $t0 and save it to $t1
bgt $t1, $t8, print # start printing prime numbers when $t1 > $t8, changed so only bgt if $t1 > square root
check: add $t2, $s2, 0 # save the bottom of stack address to $t2
sll $t3, $t0, 2 # calculate the number of bytes to jump over
sub $t2, $t2, $t3 # subtract them from bottom of stack address
add $t2, $t2, 8 # add 2 words - we started counting at 2!
lw $t3, ($t2) # load the content into $t3
beq $t3, $s0, outer # only 0's? go back to the outer loop
inner: add $t2, $s2, 0 # save the bottom of stack address to $t2
sll $t3, $t1, 2 # calculate the number of bytes to jump over
add $t4, $t1, 2 # save $t1 + 2 into $t4, added
sll $t5, $t4, 2 # mul by 4, added
sub $t2, $t2, $t3 # subtract them from bottom of stack address
add $t2, $t2, 8 # add 2 words - we started counting at 2!
sw $s0, ($t2) # store 0's -> it's not a prime number!
add $t1, $t1, $t0 # do this for every multiple of $t0
add $t1, $t1, $t0 # adding $t0 to $t1, added
sub $t2, $t2, $t5 # save $t2 - $t5 into $t2, added
add $t2, $t2, 8 # adding 8 to $t2, added
sw $s0, ($t2) # store contents of $s0 at address contained in $t2, added
add $t4, $t4, $t0 # adding $t0 to $t4, added
blt $t1, $t9, inner # every multiple done? go back to outer loop, changed to blt and branching to inner
j outer # some multiples left? go back to inner loop, changed to branching to outer
print: li $t0, 1 # reset counter variable to 1
# hard coding a 2
li $v0, 1
addi $a0, $a0, 2
syscall
# hard coding a space
li $v0, 4
la $a0, space
syscall
count: add $t0, $t0, 2 # increment counter variable (start at 2), skipping even numbers
bgt $t0, $t9, exit # make sure to exit when all numbers are done (branch to exit if $t0 > $t9)
add $t2, $s2, 0 # save the bottom of stack address to $t2
sll $t3, $t0, 2 # calculate the number of bytes to jump over
sub $t2, $t2, $t3 # subtract them from bottom of stack address
add $t2, $t2, 8 # add 2 words - we started counting at 2!
lw $t3, ($t2) # load the content into $t3
beq $t3, $s0, count # only 0's? go back to count loop
add $t3, $s2, 0 # save the bottom of stack address to $t3
sub $t3, $t3, $t2 # substract higher from lower address (= bytes)
srl $t3, $t3, 2 # changed div to srl
add $t3, $t3, 2 # add 2 (words) = the final prime number!
li $v0, 1 # system code to print integer
add $a0, $t3, 0 # the argument will be our prime number in $t3
syscall # print it!
li $v0, 4 # system code to print string
la $a0, space # the argument will be a whitespace
syscall # print it!
bne $t0, $t9, count # take loop when $t0 != $t9, changed ble to bne
exit: li $v0, 10 # set up system call 10 (exit)
syscall
【问题讨论】：
标签： mips sieve-of-eratosthenes