assembly - Display floating point by printf -


i have problem display floating point value using printf.

i'm trying display result of math function, 0.00.

could me , tell i'm doing wrong?

my gnu code:

.text text: .ascii  "function result: %4.2f \n" .data x: .float 2.0 one: .float 1.0 result: .float 0.0   format: .ascii "%f"   .global main  main: push $x push $format call scanf   finit  flds x    fmuls x     #x*x  fadds 1     fsqrt         fsub 1          fsts result  xor %eax, %eax   push $result push $text  call printf   pushl $0 call exit

in gnu assembler, $ designates literal value (a value encoded instruction). value of label address. $x, $format, $result, , $text addresses of labels; addresses have values labeling. printf not use address %f. must pass value of floating-point number, not address. and, frank kotler notes, must pass 64-bit double, not 32-bit float.

the easiest way might insert add $-8, %esp (or add %esp, $-8, depending on order of operands in assembler version) before fsts result instruction , change fsts result instruction either fst (%esp) or fstl (%esp), depending on assembler. (also, these fstp (%esp) or fstpl (%esp) pop value floating-point stack instead of leaving there.) delete push $result.

these changes allocate 8 bytes on stack (in add instruction) , store floating-point result 8 bytes.

also, expect code responsible cleaning arguments passed called routines: should add 8 stack pointer after calling scanf pop 2 arguments, , should add twelve after calling printf pop new eight-byte argument , four-byte address of format string. program may work without these changes since terminate program calling exit. however, not possible return routine ret instruction without cleaning stack.

supplement

the following code works @ ideone.com, using second choice assembler (gcc-4.7.2):

.text text: .asciz  "function result: %4.2f \n" .data x: .float 2.0 one: .float 1.0 result: .float 0.0   format: .asciz "%f"   .global main  main: push $x push $format call scanf add $8, %esp  finit  flds x    fmuls x     #x*x  fadds 1     fsqrt         fsub 1         add $-8, %esp fstpl (%esp)  xor %eax, %eax   push $text  call printf add $12, %esp   pushl $0 call exit

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