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libpgf: an API for building heaps from buffers in gu/seq.c

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kr.angelov
2012-02-29 18:51:21 +00:00
parent b727e676b4
commit 2775faad7a
3 changed files with 111 additions and 0 deletions
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6
src/runtime/c/gu/fun.h
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@@ -62,4 +62,10 @@ struct GuEquality {
bool (*is_equal)(GuEquality* self, const void* a, const void* b);
};
typedef const struct GuOrder GuOrder;
struct GuOrder {
int (*compare)(GuOrder* self, const void* a, const void* b);
};
#endif // GU_FUN_H_

91
src/runtime/c/gu/seq.c
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@@ -3,6 +3,7 @@
#include <gu/fun.h>
#include <gu/assert.h>
#include <string.h>
#include <stdlib.h>
struct GuBuf {
@@ -162,6 +163,96 @@ gu_buf_freeze(GuBuf* buf, GuPool* pool)
return seq;
}
static void
gu_heap_siftdown(GuBuf *buf, GuOrder *order, int startpos, int pos)
{
void *newitem = alloca(buf->elem_size);
memcpy(newitem, &buf->data[buf->elem_size * pos], buf->elem_size);
while (pos > startpos) {
int parentpos = (pos - 1) >> 1;
void *parent = &buf->data[buf->elem_size * parentpos];
if (order->compare(order, newitem, parent) < 0) {
memcpy(&buf->data[buf->elem_size * pos], parent, buf->elem_size);
pos = parentpos;
continue;
}
break;
}
memcpy(&buf->data[buf->elem_size * pos], newitem, buf->elem_size);
}
static void
gu_heap_siftup(GuBuf *buf, GuOrder *order, int pos)
{
int startpos = pos;
int endpos = gu_buf_length(buf);
void *newitem = alloca(buf->elem_size);
memcpy(newitem, &buf->data[buf->elem_size * pos], buf->elem_size);
int childpos = 2*pos + 1;
while (childpos < endpos) {
int rightpos = childpos + 1;
if (rightpos < endpos &&
order->compare(order,
&buf->data[buf->elem_size * childpos],
&buf->data[buf->elem_size * rightpos]) >= 0) {
childpos = rightpos;
}
memcpy(&buf->data[buf->elem_size * pos],
&buf->data[buf->elem_size * childpos], buf->elem_size);
pos = childpos;
childpos = 2*pos + 1;
}
memcpy(&buf->data[buf->elem_size * pos], newitem, buf->elem_size);
gu_heap_siftdown(buf, order, startpos, pos);
}
void
gu_buf_heap_push(GuBuf *buf, GuOrder *order, void *value)
{
memcpy(gu_buf_extend(buf), value, buf->elem_size);
gu_heap_siftdown(buf, order, 0, gu_buf_length(buf)-1);
}
void
gu_buf_heap_pop(GuBuf *buf, GuOrder *order, void* data_out)
{
const void* last = gu_buf_trim(buf); // raises an error if empty
if (gu_buf_length(buf) > 0) {
memcpy(data_out, buf->data, buf->elem_size);
memcpy(buf->data, last, buf->elem_size);
gu_heap_siftup(buf, order, 0);
} else {
memcpy(data_out, last, buf->elem_size);
}
}
void
gu_buf_heap_replace(GuBuf *buf, GuOrder *order, void *value, void *data_out)
{
gu_require(gu_buf_length(buf) > 0);
memcpy(data_out, buf->data, buf->elem_size);
memcpy(buf->data, value, buf->elem_size);
gu_heap_siftup(buf, order, 0);
}
void
gu_buf_heapify(GuBuf *buf, GuOrder *order)
{
size_t middle = gu_buf_length(buf) / 2;
for (size_t i = 0; i < middle; i++) {
gu_heap_siftup(buf, order, i);
}
}
typedef struct GuBufOut GuBufOut;
struct GuBufOut
{

14
src/runtime/c/gu/seq.h
View File

@@ -124,6 +124,20 @@ gu_buf_trim(GuBuf* buf);
void
gu_seq_resize_tail(GuSeq seq, ptrdiff_t change);
// Using a buffer as a heap
void
gu_buf_heap_push(GuBuf *buf, GuOrder *order, void *value);
void
gu_buf_heap_pop(GuBuf *buf, GuOrder *order, void* data_out);
void
gu_buf_heap_replace(GuBuf *buf, GuOrder *order, void *value, void *data_out);
void
gu_buf_heapify(GuBuf *buf, GuOrder *order);
#if 0
void
gu_buf_resize_head(GuBuf* buf, ptrdiff_t change);