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| en:multiasm:exercisebook:pc:sut:scenarios_standalone [2026/05/20 15:01] – [Displaying floating point values] ktokarz | en:multiasm:exercisebook:pc:sut:scenarios_standalone [2026/05/20 15:57] (current) – [Implementation of calculation functions] ktokarz | ||
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| - | ===== Converting integers to hex ===== | + | ====== Scenarios ====== |
| + | ===== Converting integers to hexadecimal text ===== | ||
| In our first scenario, we will modify the conversion library, adding another function which should convert integer input into a hexadecimal representation. We can copy the int_to_ascii function and introduce some simple modifications. First, we need to divide the input value by 16, not by 10. | In our first scenario, we will modify the conversion library, adding another function which should convert integer input into a hexadecimal representation. We can copy the int_to_ascii function and introduce some simple modifications. First, we need to divide the input value by 16, not by 10. | ||
| <code asm> | <code asm> | ||
| Line 182: | Line 183: | ||
| sum_6_int endp | sum_6_int endp | ||
| </ | </ | ||
| - | The stack from a function perspective looks like in a fig. | + | The stack from a function perspective looks like in a fig.{{ref> |
| + | <figure ex_stack_simple> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | |||
| + | The caller passes arguments according to the Windows x64 ABI. First four arguments through RCX, RDX, R8 and R9 registers. Further arguments are placed onto the stack. The caller is also responsible for reserving the shadow space for all arguments before the call, even those passed through registers. That's why 32 bytes are reserved before the return address is automatically placed on the stack by the call instruction. | ||
| + | |||
| + | Please note the order of arguments. It is assumed that they are placed onto the stack in reverse order. The last argument is placed on the stack first. That's why the 6th argument is at the higher address, next is the 5th argument and next there is a shadow space for arguments 1 - 4. From the perspective of a function, the first argument (or rather its shadow) is just after the return address. As the return address consumes 8 bytes, the shadow space for the first argument is at address SP+8. | ||
| + | |||
| + | How to call such a function? Putting the first four parameters into registers is quite simple. To place remaining arguments onto the stack, it is possible to use the **push** instruction. | ||
| + | <code asm> | ||
| + | ;call sum of 6 integers function | ||
| + | |||
| + | mov rcx, 1 ; 1st argmument | ||
| + | mov rdx, 2 ; 2nd argmument | ||
| + | mov r8, 3 ; 3rd argmument | ||
| + | mov r9, 4 ; 4th argmument | ||
| + | mov r11, 6 | ||
| + | push r11 ; 6th argument | ||
| + | mov r10, 5 | ||
| + | push r10 ; 5th argument | ||
| + | | ||
| + | sub rsp, 20h ; 32 bytes of the shadow space | ||
| + | | ||
| + | call sum_6_int ; function call | ||
| + | | ||
| + | add rsp, 30h ; stack cleanup | ||
| + | mov rcx, rax ; result in rax | ||
| + | </ | ||
| + | |||
| + | The figure {{ref> | ||
| + | <figure ex_stack_caller_push> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| - | The caller passes arguments according to the Windows x64 ABI. The responsibility of the caller is also to reserve the shadow space for all arguments before the call. | ||
