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Added comments to asm

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Original commit message from CVS:
Added comments to asm
This commit is contained in:
Wim Taymans 2002-12-30 23:59:59 +00:00
parent fbe8f4f657
commit aea79e82e1
1 changed files with 16 additions and 9 deletions
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25
gst/gsttrashstack.h
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@ -73,9 +73,9 @@ gst_trash_stack_push (GstTrashStack *stack, gpointer mem)
{
__asm__ __volatile__ (
"1: \n\t"
" movl %2, (%1); \n\t"
" lock; cmpxchg %1, %0; \n\t"
" jnz 1b; \n"
" movl %2, (%1); \n\t" /* mem->next == stack->head */
" lock; cmpxchg %1, %0; \n\t" /* if head unchanged, move mem into it */
" jnz 1b; \n" /* head changed, retry */
:
: "m" (*stack),
"r" (mem),
@ -88,15 +88,22 @@ gst_trash_stack_pop (GstTrashStack *stack)
{
GstTrashStackElement *head;
/* pop is a little more complicated as we need to avoid the so called ABA
* problem that arises when a pop and push of the same element happens
* right between when we read head->next and try to swing the new pointer
* into place. This is usually solved using a counter which makes it highly
* inlikely that we manage to grab the wrong head->next value.
*/
__asm__ __volatile__ (
" testl %%eax, %%eax; \n\t"
" testl %%eax, %%eax; \n\t" /* if (head == NULL) return */
" jz 20f; \n\t"
"10: \n\t"
" movl (%%eax), %%ebx; \n\t"
" movl %%edx, %%ecx; \n\t"
" incl %%ecx; \n\t"
" lock; cmpxchg8b %1; \n\t"
" jnz 10b; \n\t"
" movl (%%eax), %%ebx; \n\t" /* take value pointed to by head (head->next) */
" movl %%edx, %%ecx; \n\t" /* take counter */
" incl %%ecx; \n\t" /* and increment */
" lock; cmpxchg8b %1; \n\t" /* if eax:edx == *stack, move ebx:ecx to *stack,
* else *stack is moved into eax:edx again... */
" jnz 10b; \n\t" /* ... and we retry */
"20: \n"
: "=a" (head)
: "m" (*stack),