Florian Klaempfl a écrit :
Vincent Snijders wrote:
Hi,
Suppose I have the following code:
var
a,b: dword;
c: qword;
begin
a := 10000000;
b := 20000000;
c := a * b;
writeln(c);
end.
Now, although c is large enough to contain the result only the lower
dword is filled. I can force correct results by using c := qword(a) * b,
but the slow fpc_mul_qword is used.
The code generated for the above sample is:
# [16] c:=a*b;
movl U_P$PROJECT1_A,%edx
movl U_P$PROJECT1_B,%eax
mull %edx
movl $0,%edx
movl %eax,U_P$PROJECT1_C
movl %edx,U_P$PROJECT1_C+4
What I want is the above code, but without the "movl $0,%edx"
instruction. Is there a way to do this (wihtout using fpc_mul_qword).
Only assembler for now. Any suggestions how the compiler could be told
to generate such code?
A small function (like the one I asked for a few weeks ago :-)
that would be inlined by the compiler?
Currently I use this one
function UI32x32To64(A,B: Longword): QWord;
assembler; register; nostackframe;
asm
mull %edx
end;
It is fast but certainly much less than if it were inlined.
MM
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