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POHow to right rotate a 64-bit value efficiently in ARM7 assembler?
 

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    <p>The ARM7-command set offers efficient ways to right rotate 32-bit values by an arbitrary amount in assembler. For the 2nd operand of an operation it is even "for free" by specifying <em>ror #n</em> as shifter operand, but for 64-bit integers no direct support by the instruction set is given. Besides the special cases of rotating by 1, 31, 33 or 63 bit positions (not to mention 0 or 32), I only know how to rotate a 64-bit value using <em>four</em> instructions (it's quite easy, so I don't write it here). In the four special cases I can reduce this to three instructions, but I don't know how to do it in general. So here is my question:</p> <p>Given a 64-bit value in two registers, say R0 and R1, is it possible to right rotate this value by <em>n</em> positions (for arbitrary <em>n</em>) with just <strong>three</strong> ARM7 instructions?</p>
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