我一直在研究一个程序，它使两个32位无符号整数相乘而不使用MIPS mult（multu）或div（divu）命令。 我希望输出看起来就像multu函数一样，作为一个64位高字/低字组合。 我一直在使用模型，乘数是产品的右侧，因为：
for (i=0; i<32; i++)
{
if LSB(multiplier)==1
{
LH product += multiplicand;
}
right shift product-multiplier 1;
}
目前在我的代码中，我不确定我是否正在正确处理32位加法中的可能进位位。
无论我选择操作什么整数值，我目前的输出都是“0 0”。
在我的代码中，我调用最右边的LSB（低位字），最左边的MSB（高位字）。
我的代码：
.data
promptStart: .asciiz "This prrogram does AxB without using mult or div"
getA: .asciiz "Please enter the first number(multiplicand): "
getB: .asciiz "Please enter the second number(multiplier): "
space: .asciiz " "
result: .asciiz "The product, using my program is: "
mipMult: .asciiz "The product, using MIPs multu is: "
endLine: .asciiz "\n"
.text
main:
#"welcome" screen
li $v0,4 # code for print_string
la $a0,promptStart # point $a0 to prompt string
syscall # print the prompt
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to prompt string
syscall # print the prompt
#prompt for multiplicand
li $v0,4 # code for print_string
la $a0,getA # point $a0 to prompt string
syscall # print the prompt
#acquire multiplicand
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s0,$v0 # move the resulting int to $s0
move $s4,$s0 #copy of multiplicand to use in multu
#prompt for multiplier
li $v0,4 # code for print_string
la $a0,getB # point $a0 to prompt string
syscall # print the prompt
#acquire multiplier
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s1,$v0 # move the resulting int to $s0
move $s5,$s1 #copy of multiplier to use in multu
jal MyMult
j print
MyMult:
#$s2 -> lw product, $s1 -> hw multiplier, $s0 -> multiplicand
beq $s1, $0, done # if multiplier=0--> mult gives 0
beq $s0, $0, done
move $t0, $0 #initialize 'counter'= 31
add $t0, $t0, 31
move $s2, $0 #initialize product = 0
loopOut:
beq $t0, $0, done #loop check
andi $t1, $s1, 1 #Stores LSB(MSB?) of $s1 in $t1
bne $t1, $0, loopIn #check if LSB is equal to 1
srl $s1, $s1, 1
srl $s2, $s2, 1 #right shift product & multiplier
add $t0, $t0,-1 # counter = counter -1
j loopOut
loopIn:
addu $s2, $s2, $s0 #Lw product($s2/$s1)+= multiplicand($s0)
sltu $t2, $s2, $s0 #catch carry-out(0 or 1) and stores in $t2
srl $s1, $s1, 1
srl $s2, $s2, 1 #right shift pro-plier..how to save LSB of $s2?
#add carry-out $t2 to LSB of product $s2
addu $s2, $s2, $t0 #Is this right?
addu $t0, $t0,-1 # counter = counter -1
j loopOut
done:
jr $ra
print:
# print result string
li $v0,4 # code for print_string
la $a0,result # point $a0 to string
syscall # print the result string
# print out the result
li $v0,1 # code for print_int
move $a0,$s2 # put result in $a0
syscall # print out result
li $v0,4 # code for print_string
la $a0,space # point $a0 to string
syscall # print the result string
li $v0,1 # code for print_int
move $a0,$s1 # put result in $a0
syscall # print out result
# print the line feed
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to string
syscall # print the linefeed
doMult:
#Do same computation using Mult
multu $s4, $s5
mfhi $t0
mflo $t1
li $v0,4 # code for print_string
la $a0,mipMult # point $a0 to string
syscall
# print out the result
li $v0,1 # code for print_int
move $a0,$t0 # put high in $a0
syscall # print out result
li $v0,4 # code for print_string
la $a0,space # point $a0 to string
syscall # print the result string
# print out the result
li $v0,1 # code for print_int
move $a0,$t1 # put low in $a0
syscall # print out result
# print the line feed
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to string
syscall # print the linefeed
# All done, thank you!
li $v0,10 # code for exit
syscall # exit program
答案 0 :(得分：3)
据我所知，即使你的算法也被打破了。您应该将被乘数向左移动（用于加法），将因子移到右侧（用于位测试）。产品不应该转移。此外，被乘数需要扩展到64位，并且需要64位移位才能正确地在字边界上传输位。
.data
promptStart: .asciiz "This program does AxB without using mult or div"
getA: .asciiz "Please enter the first number(multiplicand): "
getB: .asciiz "Please enter the second number(multiplier): "
space: .asciiz " "
result: .asciiz "The product, using my program is: "
mipMult: .asciiz "The product, using MIPs multu is: "
endLine: .asciiz "\n"
.text
main:
#"welcome" screen
li $v0,4 # code for print_string
la $a0,promptStart # point $a0 to prompt string
syscall # print the prompt
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to prompt string
syscall # print the prompt
#prompt for multiplicand
li $v0,4 # code for print_string
la $a0,getA # point $a0 to prompt string
syscall # print the prompt
#acquire multiplicand
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s0,$v0 # move the resulting int to $s0
move $s5,$s0 # copy of multiplicand to use in multu
#prompt for multiplier
li $v0,4 # code for print_string
la $a0,getB # point $a0 to prompt string
syscall # print the prompt
#acquire multiplier
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s1,$v0 # move the resulting int to $s0
move $s6,$s1 # copy of multiplier to use in multu
jal MyMult
j print
MyMult:
move $s3, $0 # lw product
move $s4, $0 # hw product
beq $s1, $0, done
beq $s0, $0, done
move $s2, $0 # extend multiplicand to 64 bits
loop:
andi $t0, $s0, 1 # LSB(multiplier)
beq $t0, $0, next # skip if zero
addu $s3, $s3, $s1 # lw(product) += lw(multiplicand)
sltu $t0, $s3, $s1 # catch carry-out(0 or 1)
addu $s4, $s4, $t0 # hw(product) += carry
addu $s4, $s4, $s2 # hw(product) += hw(multiplicand)
next:
# shift multiplicand left
srl $t0, $s1, 31 # copy bit from lw to hw
sll $s1, $s1, 1
sll $s2, $s2, 1
addu $s2, $s2, $t0
srl $s0, $s0, 1 # shift multiplier right
bne $s0, $0, loop
done:
jr $ra
print:
# print result string
li $v0,4 # code for print_string
la $a0,result # point $a0 to string
syscall # print the result string
# print out the result
li $v0,1 # code for print_int
move $a0,$s4 # put result in $a0
syscall # print out result
li $v0,4 # code for print_string
la $a0,space # point $a0 to string
syscall # print the result string
li $v0,1 # code for print_int
move $a0,$s3 # put result in $a0
syscall # print out result
# print the line feed
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to string
syscall # print the linefeed
doMult:
#Do same computation using Mult
multu $s5, $s6
mfhi $t0
mflo $t1
li $v0,4 # code for print_string
la $a0,mipMult # point $a0 to string
syscall
# print out the result
li $v0,1 # code for print_int
move $a0,$t0 # put high in $a0
syscall # print out result
li $v0,4 # code for print_string
la $a0,space # point $a0 to string
syscall # print the result string
# print out the result
li $v0,1 # code for print_int
move $a0,$t1 # put low in $a0
syscall # print out result
# print the line feed
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to string
syscall # print the linefeed
# All done, thank you!
li $v0,10 # code for exit
syscall # exit program