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Hello Free Pascal<br>
<br>
I've been
programming in Object Pascal for over 15 years, and over the past few
years have started picking up Intel x86 assembly language. I am very interested in learning more about the development of Free Pascal and possibly contributing some optimisations or additional features to the units.<br>
<br>
I'd like to contribute possible improvements and optimisations to
the Math unit in particular. For example, an assembler implementation
of <span style="font-weight: bold;">DivMod</span> (using the standard register parameter convention and <span style="font-weight: bold;">{$ASMMODE Intel}</span>)
- apologies if I got the code slightly wrong... I had to port it from
another function where the arrangement of the parameters were different
in that the Result parameter was actually a function result (and hence
could be written to EAX), while Remainder was referenced in ECX rather
than on the stack:<br>
<br>
<pre style="margin: 0; padding: 0;"><code class="bbc_code"><span style="font-weight: bold;">procedure</span> DivMod(Dividend: DWord; Divisor: DWord; <span style="font-weight: bold;">var</span> Result, Remainder: DWord); <span style="font-weight: bold;">assembler;
asm</span>
{$IFDEF CPU64}
MOV R10, RDX
MOV RAX, RCX
XOR RDX, RDX { Zero RDX because the DIV operation uses RDX:RAX as the numerator }
DIV R10 { After this call, quotient is in RAX and remainder is in RDX }
MOV [R8], RAX
MOV [R9], RDX
{$ENDIF}
{$IFDEF CPU32}
PUSH EBX
MOV EBX, EDX
XOR EDX, EDX { Zero EDX because the DIV operation uses EDX:EAX as the numerator }
DIV EBX { After this call, quotient is in EAX and remainder is in EDX }
MOV EBX, [ESP+4] { Since we pushed EBX onto the stack, the address to "Remainder" is one step back }
MOV [ECX], EAX
MOV [EBX], EDX
POP EBX
{$ENDIF}
<span style="font-weight: bold;">end;</span></code></pre><br>
It was mentioned in the comments of <span style="font-weight: bold;">DivMod</span> that a compiler directive could be used (e.g. FPC_MATH_HAS_CPUDIVMOD) to run assembler versions of these functions, so the above would be a first preliminary suggestion (Intel x86/x64 assember definitely has it, with DIV defined to return the quotient in EAX and the remainder in EDX).<br>
<br>
I would also like to suggest including an <span style="font-weight: bold;">IncMod</span>
function (which effectively calculates "Value := (Value + 1) mod Divisor"),
which has uses in certain mathematical and cryptographic fields and
could be written very efficiently in assembly language (e.g. ADD EAX, 1;
CMP EAX, EDX ... and then setting EAX to zero if the zero flag is set). In a similar vein, an <span style="font-weight: bold;">ISqrt</span> function might have some uses as well (or just an overloaded version of <span style="font-weight: bold;">sqrt</span> that takes an unsigned integer parameter and result), and there are algorithms that can calculate the integer portion of the answer far, far faster than a floating-point square root. Would these be viable additions and improvements?<br>
<br>
Apologies if this isn't the best place to be submitting suggestions - I'm still learning the system.<br>
<br>
Yours faithfully,<br>
<br>
J. Gareth Moreton aka. Curious Kit<br>
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