75 lines
1.9 KiB
C
75 lines
1.9 KiB
C
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// generic intrusive FIFO queue
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#ifndef QUEUE_H
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#define QUEUE_H
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#include <stdbool.h>
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#include <SDL2/SDL_assert.h>
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// To define a queue type of "struct foo":
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// struct queue_foo QUEUE(struct foo);
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#define QUEUE(TYPE) { \
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TYPE *first; \
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TYPE *last; \
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}
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#define queue_init(PQ) \
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(void) ((PQ)->first = NULL)
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#define queue_is_empty(PQ) \
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!(PQ)->first
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// NEXTFIELD is the field in the ITEM type used for intrusive linked-list
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//
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// For example:
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// struct foo {
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// int value;
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// struct foo *next;
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// };
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//
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// // define the type "struct my_queue"
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// struct my_queue QUEUE(struct foo);
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//
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// struct my_queue queue;
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// queue_init(&queue);
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//
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// struct foo v1 = { .value = 42 };
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// struct foo v2 = { .value = 27 };
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//
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// queue_push(&queue, next, v1);
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// queue_push(&queue, next, v2);
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//
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// struct foo *foo;
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// queue_take(&queue, next, &foo);
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// assert(foo->value == 42);
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// queue_take(&queue, next, &foo);
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// assert(foo->value == 27);
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// assert(queue_is_empty(&queue));
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//
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// push a new item into the queue
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#define queue_push(PQ, NEXTFIELD, ITEM) \
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(void) ({ \
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(ITEM)->NEXTFIELD = NULL; \
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if (queue_is_empty(PQ)) { \
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(PQ)->first = (PQ)->last = (ITEM); \
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} else { \
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(PQ)->last->NEXTFIELD = (ITEM); \
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(PQ)->last = (ITEM); \
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} \
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})
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// take the next item and remove it from the queue (the queue must not be empty)
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// the result is stored in *(PITEM)
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// (without typeof(), we could not store a local variable having the correct
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// type so that we can "return" it)
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#define queue_take(PQ, NEXTFIELD, PITEM) \
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(void) ({ \
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SDL_assert(!queue_is_empty(PQ)); \
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*(PITEM) = (PQ)->first; \
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(PQ)->first = (PQ)->first->NEXTFIELD; \
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})
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// no need to update (PQ)->last if the queue is left empty:
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// (PQ)->last is undefined if !(PQ)->first anyway
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#endif
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