On Tue, May 24, 2011 at 10:04 AM, David Henningsson
david.hennings...@canonical.com wrote:
Ok, so there is still a high-pitched noise with 5.1, although I tried to fix
that a while ago. I now know what the error is, but perhaps somewhat with
more GCC-ASM skills can help me fix it.
I spent parts of yesterday and today analysing it and came up with the
following conclusion:
Here's the asm code as written in svolume_sse.c, function
pa_volume_s16ne_sse2:
#define MOD_ADD(a,b) \
add #a, %3 \n\t /* channel += inc */ \
mov %3, %4 \n\t \
sub #b, %4 \n\t /* tmp = channel - channels */ \
cmovae %4, %3 \n\t /* if (tmp = 0) channel = tmp */
And called with: MOD_ADD($8, %5)
Here's what it shows up with gdb (on i386) :
0x00f3fbe6 +550: add $0x8,%edi
0x00f3fbe9 +553: mov %edi,%ecx
0x00f3fbeb +555: sub %edi,%ecx
0x00f3fbed +557: cmovae %ecx,%edi
The error: both %3 and %5 is turned into the %edi register.
Here's the register allocation:
: +r (samples), +r (volumes), +r (length), =D (channel), =r
(temp)
: rm ((pa_reg_x86)channels)
: cc
As I can tell from the above the =D forces %3 to go into %edi, but I don't
know how to tell GCC not to use %edi for %5 (channels) as well, does anybody
know? Can this be a GCC bug?
Either use +D for channel or rm for channels.
The manual here:
http://gcc.gnu.org/onlinedocs/gcc/Modifiers.html#Modifiers
is pretty good.
--Andy
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