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As an extra point, removing the 'skip' check (i.e. cmp ax, $3FE0, jbe @@skip) removes 6 bytes from the code size and shaves about 2 to 3 nanoseconds off the execution time in most cases, and it could be argued that it's worth going for the 'no skip' version because using Frac on a value of x where |x| < 1 is rather uncommon compared to when |x| >= 1.<br>
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However, when running my timing tests, one thing that's confused me is that when using very large inputs like 10^300, the function is at least 5 nanoseconds slower than FracSkip2, even though the code is less complex. This happens even if I put 'align 16' before the @@zero label.<br>
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I did wonder if it being a debug build caused some issues, but when I compiled it with full optimisation, both versions of the functions ran slower for numbers of that size (and the original FracDoSkip took about just as long), and SafeFrac beat them by around 5 nanoseconds.<br>
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Nevertheless, I conclude that for most situations, using the improved FracNoSkip gives the best performance and size for typical inputs, but this may depend on an individual machine's architecture.<br>
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function FracNoSkp2(const X: ValReal): ValReal; assembler; nostackframe;<br>
asm<br>
movq rax, xmm0<br>
shr rax, 48<br>
and ax, $7FF0<br>
cmp ax, $4330<br>
jge @@zero<br>
cvttsd2si rax, xmm0<br>
cvtsi2sd xmm4, rax<br>
subsd xmm0, xmm4<br>
ret<br>
@@zero:<br>
xorpd xmm0, xmm0<br>
end;<br>
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****<br>
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Note: 'align 16' at the start of a procedure is usually unnecessary, as FPC aligns procedures to 16-byte boundaries automatically. FracNoSkp2 has a code size of 39 bytes, so will fill 48 bytes (3 blocks), which is a block smaller than the original FracNoSkip and the current Frac function.<br>
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I've attached my test project to this e-mail if you wish to look at the figures yourselves (I hope attachments work) and make a more informed decision. This will currenly only run on Windows due to the use of QueryPerformanceCounter for timing checks. These calls will need to be removed to run this on Linux.<br>
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Gareth aka. Kit<br>
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