I am stuck at a simple homework on 32bit machine read write cycle

A read from or write to memory on a 32bit machine is done at 4 byte per cycle , if I have an integer and a long double variables assigned with some values, then how many cycles does it take to开发者_如何转开发 read/write them ? Does it make any difference if I use these variables on different platforms et machines ? Thank you.

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Find out how how many bytes is the integer and the long double in your case. Then use the rule of three to compute how long it takes.

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On x86 32 bit sizes are as such Integer 4 bytes, long double is actually 16 bytes (at least it should be, on some arch's its 8 bytes and on others 12 bytes) and each cycle can only operate on 4 bytes at a time so Integer takes 1 cycle and long double takes 4 (3 and 2 respectively for the other sizes mentioned) cycles. On 64 bit machines with SSE instructions can do 16 bytes in one or two cycles.

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There's a good question on this topic found here: long long implementation in 32 bit machine The highest rated response has insights into how they're stored, and operated upon as well.

Since I don't know what architecture you're referring to, and since it's just homework, I am tempted to say it'll take two mov instructions to perform storing a long long integer. And thus, two cycles.

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Integer = 4 byte, long double = 10 byte which means integer = 1 cycle long double = 2.5(3?) cycles.