Given a DNA strand, return its RNA complement (per RNA transcription).
Both DNA and RNA strands are a sequence of nucleotides.
The four nucleotides found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).
The four nucleotides found in RNA are adenine (A), cytosine (C), guanine (G) and uracil (U).
Given a DNA strand, its transcribed RNA strand is formed by replacing each nucleotide with its complement:
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
# # Test transcribe_rna with some examples # # a0 - pointer to input string, for callee # a1 - pointer to output string, for callee # s0 - num of tests left to run # s1 - address of input string # s2 - address of expected output string # s3 - char byte of input # s4 - char byte of output # s5 - counter for clearing output # # transcribe_rna must: # - be named transcribe_rna and declared as global # - read input address of string from a0 # - follow the convention of using the t0-9 registers for temporary storage # - (if it uses s0-7 then it is responsible for pushing existing values to the stack then popping them back off before returning) # - write a zero-terminated string representing the return value to address given in a1 .data # number of test cases n: .word 5 # input values and expected output values (all null terminated) ins: .asciiz "C", "G", "T", "A", "ACGTGGTCTTAA" outs: .asciiz "G", "C", "A", "U", "UGCACCAGAAUU" failmsg: .asciiz "failed for test input: " expectedmsg: .asciiz ". expected " tobemsg: .asciiz " to be " okmsg: .asciiz "all tests passed" .text runner: lw $s0, n la $s1, ins la $s2, outs li $v0, 9 # code for allocating heap memory li $a0, 16 # specify 16 bytes - length of longest expected output syscall move $a1, $v0 # location of allocated memory is where callee writes result run_test: jal clear_output # zero out output location move $a0, $s1 # move address of input str to a0 jal transcribe_rna # call subroutine under test move $v1, $a1 # retain a copy of response from callee scan: lb $s3, 0($s2) # load one byte of the expectation lb $s4, 0($v1) # load one byte of the actual bne $s3, $s4, exit_fail # if the two differ, the test has failed addi $s2, $s2, 1 # point to next expectation byte addi $v1, $v1, 1 # point to next actual byte addi $s1, $s1, 1 # point to next input byte bne $s3, $zero, scan # if one char (and therefore the other) was not null, loop done_scan: sub $s0, $s0, 1 # decrement num of tests left to run bgt $s0, $zero, run_test # if more than zero tests to run, jump to run_test exit_ok: la $a0, okmsg # put address of okmsg into a0 li $v0, 4 # 4 is print string syscall li $v0, 10 # 10 is exit with zero status (clean exit) syscall exit_fail: la $a0, failmsg # put address of failmsg into a0 li $v0, 4 # 4 is print string syscall move $a0, $s1 # print input that failed on li $v0, 4 syscall la $a0, expectedmsg li $v0, 4 syscall move $a0, $v1 # print actual that failed on li $v0, 4 syscall la $a0, tobemsg li $v0, 4 syscall move $a0, $s2 # print expected value that failed on li $v0, 4 syscall li $a0, 1 # set error code to 1 li $v0, 17 # 17 is exit with error syscall clear_output: sw $zero, 0($a1) # zero out output by storing 4 words (16 bytes) of zeros sw $zero, 4($a1) sw $zero, 8($a1) sw $zero, 12($a1) jr $ra # # Include your implementation here if you wish to run this from the MARS GUI. # .include "impl.mips"
.globl transcribe_rna # I noticed that: # - A,G,C,U are all odd numbers # - to transcribe, all you need to do is toggle the third bit (0x04) # - and IF it's U, we have to set the 5th bit (0x45 -> 0x55) # To make good use of these observations, we have to normalise AGCT to be all in # the 0x4[odd] form. This allows the loop to branch only once instead of 3 times .text transcribe_rna: move $a2, $a1 #incrementable ptr for a1 LOOP: lb $t0, ($a0) beqz $t0, STOP or $t0, $t0, 0x01 # if 0x54 make it 0x55 and $t0, $t0, 0xef # if 0x5* make it 0x4* xor $t0, $t0, 0x04 # do the transformation beq $t0, 0x45, fix_u # A -> U(0x55) instead of E(0x45) j store_t0 fix_u: or $t0, $t0, 0x10 store_t0: sb $t0, ($a2) addi $a0, $a0, 1 addi $a2, $a2, 1 j LOOP STOP: jr $ra
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.