In this lab, we write function binary_search in RISC-V. The prototype of the function and an implementation in C is at the end of this page. Translate the C code at the bottom of the page to RISC-V assembly code. The skeleton code is in lab4.s. Function binary_search is located at the end of the file. It is empty in the skeleton code. There are some constraints/tips. 1. To ensure we do not use pseudoinstructions, we turn off the feature in RARS. In Settings, uncheck "Permit extended (pseudo) instructions and formats". 2. Follow the C code closely. Although binary search is simple, it is very easy to make mistakes if you have not written it many times. 3. We keep variable left in register s1. Other local variables do not have to be in a saved register. Think about why we need to keep left, but not other variables, in a saved register. 4. There should be only one exit (one return instruction) in the function. In the C code, we use goto f_exit on purpose. With one exit, we do not have multiple copies of clean up code, e.g., restoring saved registers. 5. There is an IF-ELSEIF-ELSE structure. Write the outline first, without instructions in each branch. Follow the order of branches in C code: IF branch, then the ELSEIF branch, and finally the ELSE branch. It is easier to check the code this way. 6. There is only one LW instruction, for reading a [half], between the code that saves/restores registers. 7. During the execution of the program, examine how ra and sp registers are changed and what have been saved on the stack. It helps to understand how funciton and local storage works.

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In this lab, we write function binary_search in RISC-V. The prototype of the function and an implementation in C is at the end of this page.
Translate the C code at the bottom of the page to RISC-V assembly code.
The skeleton code is in lab4.s. Function binary_search is located at the end of the file. It is empty in the skeleton code.
There are some constraints/tips.
1. To ensure we do not use pseudoinstructions, we turn off the feature in RARs. In Settings, uncheck "Permit extended (pseudo)
instructions and formats".
2. Follow the C code closely. Although binary search is simple, it is very easy to make mistakes if you have not written it many times.
3. We keep variable left in register s1. Other local variables do not have to be in a saved register. Think about why we need to keep
left, but not other variables, in a saved register.
4. There should be only one exit (one return instruction) in the function. In the C code, we use goto f_exit on purpose. With one exit,
we do not have multiple copies of clean up code, e.g., restoring saved registers.
5. There is an IF-ELSEIF-ELSE structure. Write the outline first, without instructions in each branch. Follow the order of branches in C
code: IF branch, then the ELSEIF branch, and finally the ELSE branch. It is easier to check the code this way.
6. There is only one LW instruction, for reading a [half], between the code that saves/restores registers.
7. During the execution of the program, examine how ra and sp registers are changed and what have been saved on the stack. It helps
to understand how funciton and local storage works.
Transcribed Image Text:In this lab, we write function binary_search in RISC-V. The prototype of the function and an implementation in C is at the end of this page. Translate the C code at the bottom of the page to RISC-V assembly code. The skeleton code is in lab4.s. Function binary_search is located at the end of the file. It is empty in the skeleton code. There are some constraints/tips. 1. To ensure we do not use pseudoinstructions, we turn off the feature in RARs. In Settings, uncheck "Permit extended (pseudo) instructions and formats". 2. Follow the C code closely. Although binary search is simple, it is very easy to make mistakes if you have not written it many times. 3. We keep variable left in register s1. Other local variables do not have to be in a saved register. Think about why we need to keep left, but not other variables, in a saved register. 4. There should be only one exit (one return instruction) in the function. In the C code, we use goto f_exit on purpose. With one exit, we do not have multiple copies of clean up code, e.g., restoring saved registers. 5. There is an IF-ELSEIF-ELSE structure. Write the outline first, without instructions in each branch. Follow the order of branches in C code: IF branch, then the ELSEIF branch, and finally the ELSE branch. It is easier to check the code this way. 6. There is only one LW instruction, for reading a [half], between the code that saves/restores registers. 7. During the execution of the program, examine how ra and sp registers are changed and what have been saved on the stack. It helps to understand how funciton and local storage works.
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