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How many x86 instructions?
On 20/02/2014 11:21 PM, Paul wrote:
At one time, a compiler would issue instructions from about 30% of the instruction set. It would mean a compiled program would never emit the other 70% of them. But a person writing assembler code, would have access to all of them, at least, as long as the mnemonic existed in the assembler. I think the original idea of the x86's large instruction count was to make an assembly language as full-featured as a high-level language. x86 even had string-handling instructions! I remember I designed an early version of the CPUID program that ran under DOS. The whole executable including its *.exe headers was something like 40 bytes! Got it down to under 20 bytes when I converted it to *.com (which had no headers)! Most of the space was used to store strings, like "This processor is a:" followed by generated strings like 386SX or 486DX, etc. You could make some really tiny assembler programs on x86. Of course, compiled programs ignored most of these useful high-level instructions and stuck with simple instructions to do everything. Yousuf Khan |
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