装配印刷浮动 [英] assembly printing float

问题描述

我在遇到一些麻烦，在装配以下操作。
我正在组装IA32。假设-4（％EBP）= x和-8（％EBP）= y和我得到他们的用户已。
这是code：

I'm having some troubles with the following actions in assembly. I'm working on assembly IA32. Assume -4(%ebp)=x and -8(%ebp)=y and I get them from user already. this is the code:

format1:    .string "Multiply : %u * %u = %llu\n"
format2:    .string "Divide : %u / %u = %u\n"

# operation multiply
movl    -4(%ebp),   %eax
mull    -8(%ebp)
pushl   %edx
pushl   %eax
pushl   -8(%ebp)
pushl   -4(%ebp)
pushl   $format1
call    printf

# operation divide
movl    -4(%ebp),    %eax   
divl    -8(%ebp)
pushl    %eax
pushl   -8(%ebp)
pushl   -4(%ebp)
pushl   $format2
    call    printf

究其原因，乘法的结果是LLU％，是因为我希望能够乘2长数字，并打印出结果，即使达到64字节。
而且，在％EDX马尔命令保存64字节结果的其他32个字节，所以我需要把它推到堆栈，以及对printf的。
例如我想这样的输出：

The reason the result of the multiply is in %llu is because I want to be able to multiply 2 long numbers and print the result even if it reaches 64 bytes. And also that in %edx the mull command saves the "other 32 bytes" of the 64 byte result, so I need to push it to the stack as well for the printf. e.g. I want this output:

 Multiply : 4000000000 * 2 = 16000000000

另外，我要的3 4除法运算返回X.YZ结果。 （不超过2号中的尾数，和没有四舍五入）
例如。

Also, I want the divide operation of 3 with 4 to return X.YZ result. (no more than 2 numbers in the mantissa, and no rounding off) e.g.

Divide : 3 / 4 = 0.75

19和1000：

for 19 and 1000:

Divide : 19 / 1000 = 0.01

和为8和2：

Divide : 8 / 2 = 4.00

我真的努力了很多得到的结果，但没有成功。
非常感谢！ ：）

I really tried alot to get the result but no success. thanks ALOT! :)

推荐答案

是的，当然你也可以使用 scanf函数，只是通过正确的参数。
如你已被告知，对于浮点结果，你需要使用一些浮点除法和打印的浮点格式。

Yes, of course you can use scanf, just pass the correct arguments. As you have been told, for floating point result you need to use some floating point divide and a floating point format for printing.

请注意，根据调用约定，你应该$ EBX 的对$ pserve寄存器的值。此外，你应该保持堆栈平衡和preferably对齐。

Note that according to calling convention, you should preserve value of ebx register. Furthermore, you should keep stack balanced, and preferably aligned.

一个可能的解决方案：

.comm x,4,4
.comm y,4,4

.section    .rodata

format1:    .string "Div : %d / %d = %g\n"
format2:    .string "Mod : %d %% %d = %d\n"
format3:    .string "%d %d"

.text
.globl  main
.type   main, @function
main:
    subl $32, %esp # allocate space, preserve alignment

    movl $format3, (%esp)
    movl $x, 4(%esp)
    movl $y, 8(%esp)
    call scanf

# operation divide
    fildl x
    fidivl y
    fstpl 12(%esp) # x / y

    movl $format1, (%esp)
    movl x, %eax
    movl %eax, 4(%esp)
    movl y, %eax
    movl %eax, 8(%esp)
    call printf

# operation modulo
    movl x, %eax
    cltd
    idivl y
    movl $format2, (%esp)
    movl x, %eax
    movl %eax, 4(%esp)
    movl y, %eax
    movl %eax, 8(%esp)
    movl %edx, 12(%esp)
    call printf

    addl $32, %esp
    xor %eax, %eax
    ret

查看 code运行。

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