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When performing division on ARM, this is the code snippet that I encountered.

   0x83d8 <main+12>:    mov r3, #10
   0x83dc <main+16>:    str r3, [r11, #-8]
   0x83e0 <main+20>:    ldr r3, [r11, #-8]
=> 0x83e4 <main+24>:    ldr r2, [pc, #40]   ;; 0x8414 <main+72>
   0x83e8 <main+28>:    smull   r1, r2, r2, r3
   0x83ec <main+32>:    asr r3, r3, #31
   0x83f0 <main+36>:    rsb r3, r3, r2
   0x83f4 <main+40>:    str r3, [r11, #-8]

In the original program, I store the value 10 to a variable, divide it by 3 and store it in the same variable.

[r11, #-8] in the above example has the value 0xa. After 0x83e4, r2 is loaded up as 0x55555556. My doubts are as follows :-

  1. Is this a common way of performing division without the div instruction?
  2. What are the other ways you have encountered in which division is performed without using an instruction that performs division?

1 Answers1

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Optimizing compilers will typically use the method above for compiling division by a constant.

You can read more about it at the following links:

Glorfindel
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Jason Geffner
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