Yes, I missed my lessons in clear communication.
-------------------------------------------------
+ The complete source files.
-------------------------------------------------
import std.stdio;
void calculate1(float a, float b)
{
float s1 = 1.0f - a;
float s2 = a * b;
writeln(s2);
writeln(a * b);
}
void calculate2(float a, float b)
{
float s1 = 1.0 - a;
float s2 = a * b;
writeln(s2);
writeln(a * b);
}
void calculate3(double a, double b)
{
double s1 = 1.0 - a;
double s2 = a * b;
writeln(s2);
writeln(a * b);
}
int main()
{
writeln("calculate1:");
calculate1(0.75f,2.0f);
writeln("calculate2:");
calculate2(0.75f,2.0f);
writeln("calculate3:");
calculate3(0.75f,2.0f);
return 0;
}
-------------------------------------------------
+ The complete output
-------------------------------------------------
calculate1:
1.5
1.5
calculate2:
0
1.5
calculate3:
1.5
1.5
-------------------------------------------------
+ Compiler
-------------------------------------------------
DMD64 D Compiler v2.057
Copyright (c) 1999-2011 by Digital Mars written by Walter Bright
Documentation: http://www.digitalmars.com/d/2.0/index.html
Usage:
This is from the downloaded zip file.
I'm using eclipse to compile it. Added the -debug.
-------------------------------------------------
+ Ubuntu 11.10 64 bit
-------------------------------------------------
uname -r
3.0.0-15-generic
-------------------------------------------------
+ BEHAVIOUR
-------------------------------------------------
As for the behaviour on 32 bit. I wish
somebody else would do it. :-)
In the previous message here below is the assembly
output of calculate2. Pay close attention to the
cvtss2sd, the cvtsd2ss and the mulss.
float s1 = 1.0 - a;
float s2 = a * b;
It converts the float a to double precision.
then performs the s1 calculation.
Then does the s2 calculation with the high
precision a and the normal float b.
Also it performs the "cvtsd2ss %xmm2,%xmm2"
for no reason at all. As it is no longer used
in the rest the code.
-------------------------------------------------
+ objdump -S test1.o
-------------------------------------------------
0000000000000000 <_D4main10calculate2FffZv>:
0: 55 push %rbp
1: 48 8b ec mov %rsp,%rbp
4: 48 83 ec 20 sub $0x20,%rsp
8: f3 0f 11 45 f0 movss %xmm0,-0x10(%rbp)
d: f3 0f 11 4d f8 movss %xmm1,-0x8(%rbp)
12: 48 b8 00 00 00 00 00 movabs $0x3ff0000000000000,%rax
19: 00 f0 3f
1c: 48 89 45 e0 mov %rax,-0x20(%rbp)
20: f2 0f 10 55 e0 movsd -0x20(%rbp),%xmm2
25: f3 0f 5a c9 cvtss2sd %xmm1,%xmm1
29: f2 0f 5c d1 subsd %xmm1,%xmm2
2d: f2 0f 5a d2 cvtsd2ss %xmm2,%xmm2
31: f3 0f 59 c8 mulss %xmm0,%xmm1
35: f3 0f 11 4d e8 movss %xmm1,-0x18(%rbp)
3a: f3 0f 10 45 e8 movss -0x18(%rbp),%xmm0
3f: e8 00 00 00 00 callq 44 <_D4main10calculate2FffZv+0x44>
44: f3 0f 10 45 f8 movss -0x8(%rbp),%xmm0
49: f3 0f 10 4d f0 movss -0x10(%rbp),%xmm1
4e: f3 0f 59 c1 mulss %xmm1,%xmm0
52: e8 00 00 00 00 callq 57 <_D4main10calculate2FffZv+0x57>
57: c9 leaveq
58: c3 retq
59: 90 nop
5a: 90 nop
5b: 90 nop
I'm going to eat now.
On 01/24/2012 05:01 PM, dennis luehring wrote:
can you give us a complete out-of-the-box compileable example (with
imports,main,etc.) with both examples the working/and nonworking
does it work correct with dmd(32bit)?
is this "calculate2" needed to reproduce the behavior?
and what compiler did you test: dmd64, (dmd32?), ...?
Am 24.01.2012 16:20, schrieb sclytrack:
void calculate2(float a, float b)
{
float s1 = 1.0 - a;
float s2 = a * b;
writeln(s2);
writeln(a * b);
}
----------------
Output:
t*b= 0
t*b= 1.5
----------------
assume CS:.text._D4main10calculate2FffZv
_D4main10calculate2FffZv:
push RBP
mov RBP,RSP
sub RSP,020h
movss -010h[RBP],XMM0
movss -8[RBP],XMM1
mov RAX,03FF0000000000000h
mov -020h[RBP],RAX
movsd XMM2,-020h[RBP]
cvtss2sd XMM1,XMM1
subsd XMM2,XMM1
------conversion but xmm2 is no longer used
cvtsd2ss XMM2,XMM2
------precision error multiplication
mulss XMM1,XMM0
movss -018h[RBP],XMM1
movss XMM0,-018h[RBP]
call _D3std5stdio14__T7writelnTfZ7writelnFfZv@PC32
movss XMM0,-8[RBP]
movss XMM1,-010h[RBP]
mulss XMM0,XMM1
call _D3std5stdio14__T7writelnTfZ7writelnFfZv@PC32
leave
ret
nop
nop
nop
------------
DMD64 D Compiler v2.057
Ubuntu 11.10
