22 Jan
2005
22 Jan
'05
5:40 p.m.
On Sat, 22 Jan 2005 18:36:46 +1100
Erik de Castro Lopo <erikd-lad(a)mega-nerd.com> wrote:
On Fri, 21 Jan 2005 23:08:50 +0000
Neil Klepeis <nklepeis(a)sbcglobal.net> wrote:
OK, the code of interest is in the process() method of the allpass class.
This method is defined as an inline function in allpass.h. I therefore
wrote a small test file :
#include "allpass.h"
static allpass ap ;
float test (float x)
{ return ap.process (x) ;
}
and compiler that with:
g++ -S -O3 test.cpp -o test.s
In the asembler output file we get this:
.LFE6:
.size _Z41__static_initialization_and_ <snip rest of line>
.section .rodata.cst4,"aM",@progbits,4
.align 4
.LC0:
.long 201326592
.text
.align 2
.p2align 4,,15
The long above (201326592) is the integer representation of the float value.
The asm code for the test function looks like this (comments added):
.globl _Z4testf
.type _Z4testf, @function
_Z4testf:
.LFB7:
pushl %ebp
.LCFI2:
movl %esp, %ebp
.LCFI3:
subl $4, %esp
.LCFI4:
flds .LC0 ; load the float value to the fpu stack
movl ap+12, %edx
movl ap+4, %ecx
flds 8(%ebp)
movl (%ecx,%edx,4), %eax ; load buffer[bufidx] -> %eax
movl %eax, -4(%ebp) ; move %eax -> bufout
flds -4(%ebp) ; load bufout to the fpu
fadd %st(2), %st ; new top of stack = bufout + the_const
fstps -4(%ebp) ; store top of stack -> bufout
flds -4(%ebp) ; load buf out to top of stack
fsubp %st, %st(2) ; new top of stack <- bufout - the_const
and so on. This shows that even with -O3, the denormalisation
code is not being optimised out.
Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo nospam(a)mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"O'Caml ... a "language designed for smart people" if there ever
was one." -- Mike Vanier
What exactly am I looking for?
I'm not too sure, but I'd know if I saw it :-).
After using g++ -S, the allpass.o file,
for example, starts out with:
Send me the whole allpass.c file by private mail (address below) and
I'll have a look.