Merge code done.
We need to do the output phase.
diff --git a/Makefile b/Makefile
index 27fbc86..bf373a8 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@
MAINO = $(patsubst %.c,%.o,$(MAIN))
DEPS = $(patsubst %.c,%.d,$(SRCS) $(MAIN))
EXECS = $(patsubst %.c,%,$(MAIN))
-FLAGS = -std=c99 -Wall
+FLAGS = -std=c99 -Wall -g
all : $(EXECS)
clean :
rm -f $(OBJS) $(DEPS) $(MAINO) $(EXECS)
diff --git a/median.c b/median.c
index 6c413ef..1dad56d 100644
--- a/median.c
+++ b/median.c
@@ -1,7 +1,9 @@
#include "median.h"
#include "hex.h"
-#include <strings.h>
-#include <stdio.h>
+#include <strings.h> // size_t
+#include <stdio.h> // fprintf
+#include <stdlib.h> // qsort
+#include <string.h> // memcpy
// The structure of the data buffer is this:
// ----------------------------------------------------------------------------
@@ -15,6 +17,7 @@
size_t nLevels; // Number of buffers available.
size_t nMembers; // The number of members in each block.
size_t currentBufferIdx; // The index of the currently active buffer.
+ size_t spareSize; // How much spare space is there in the buffer.
unsigned char data[0]; // The start of the data.
} metadata_t;
@@ -51,6 +54,12 @@
return sizeof(metadata_t) + m->nLevels * blocksize(m);
}
+// This is largely so that the "output" function
+// can be run without ruining the buffer.
+size_t sparespace(metadata_t * m) {
+ return 2 * buffersize(m);
+}
+
// Returns the first byte address which is out of bounds.
unsigned char * out_of_bounds(metadata_t * m) {
return m->data + buffersize(m) - sizeof(blockdata_t);
@@ -66,6 +75,11 @@
return (get_current_block(m)->occupancy < m->nMembers);
}
+// First byte of the spare space.
+void * spare_space(metadata_t * m) {
+ return out_of_bounds(m);
+}
+
// This will only be called in a safe situation. It's an internal function.
// Does not bound check!
// Do not call it unless you know what you are doing.
@@ -90,14 +104,118 @@
idx++;
}
}
+ // Failed to find an empty block.
return 0;
}
-unsigned int create_empty_block(metadata_t * m) {
- // TODO
+// A simple compare operator for the qsort routine.
+int compare_data(const void *a, const void *b){
+ median_data_t * i = (median_data_t *)a;
+ median_data_t * j = (median_data_t *)b;
+ return (*i < *j)?-1:+1;
+}
+
+unsigned int merge_blocks(metadata_t *m,blockdata_t *i,blockdata_t *j){
+ // Prepare an array for the data.
+ unsigned char * d = (unsigned char *)spare_space(m);
+ size_t datasz = m->nMembers * sizeof(median_data_t);
+ bzero(d, 2*datasz);
+
+ // This is the size of the data.
+ // Copy the data to where it needs to be.
+ memcpy(d, i->data, datasz);
+ memcpy(d + datasz, j->data, datasz);
+
+ // Sort it. In principle we do not need to
+ // sort things, instead we should only sort
+ // when level is 0 and merge otherwise.
+ // For now, since most of the time, we will
+ // be consuming level 0 buffers, I have left this
+ // inefficiency in.
+ // But we should fix it.
+ qsort(d,2*m->nMembers,sizeof(median_data_t),&compare_data);
+ median_data_t * sorted_data = (median_data_t *)d;
+
+ // Now interleave the sorted buffer.
+ // We should track parity and take the
+ // odd and even values alternately for each
+ // merge.
+ for(size_t idx = 0; idx < 2*m->nMembers; idx+=2){
+ i->data[idx/2] = sorted_data[idx];
+ }
+
+ // Update the metadata. i is full, j is empty.
+ // half the items are gone.
+ i->level++;
+ j->level = 0;
+ j->occupancy = 0;
+ bzero(j->data, datasz);
+ return 1;
+}
+
+// Find the smallest level such that there are two blocks at the same level.
+unsigned int identify_qualified_level(metadata_t *m, size_t *lvl) {
+ // Zero out the count buffer.
+ size_t * levelcount = (size_t *)spare_space(m);
+ bzero(levelcount, m->nLevels * sizeof(size_t));
+ // Iterate over the blocks, and count up the blocks at each level.
+ for(unsigned char * ptr = (unsigned char *) m->data; // Start of the data blocks.
+ ptr <= (m->data + buffersize(m) - blocksize(m)); // The next block will fit into the buffer.
+ ptr += blocksize(m)) { // Advance by a block
+ blockdata_t * b = (blockdata_t*) ptr;
+ levelcount[b->level]++;
+ }
+ // Look for a level where the count is at least 2.
+ for(size_t idx = 0; idx < m->nLevels; idx++) {
+ if(levelcount[idx] > 1) {
+ // Found one, return it.
+ *lvl = idx;
+ return 1;
+ }
+ }
+ // There is no such thing.
return 0;
}
+unsigned int identify_compatible_block_pair(metadata_t *m, blockdata_t ** i, blockdata_t ** j) {
+ size_t qualified_level;
+ // Initial values to return.
+ *i = 0;
+ *j = 0;
+ // Find the qualified level.
+ if (!identify_qualified_level(m,&qualified_level)) {
+ return 0;
+ }
+ // State machine to find the two buffers.
+ for(unsigned char * ptr = (unsigned char *) m->data; // Start of the data blocks.
+ ptr <= (m->data + buffersize(m) - blocksize(m)); // The next block will fit into the buffer.
+ ptr += blocksize(m)) { // Advance by a block
+ blockdata_t * b = (blockdata_t*) ptr;
+ if (!(*i) && (b->level == qualified_level)) {
+ // Found the first one.
+ *i = b;
+ continue;
+ }
+ if (!(*j) && (b->level == qualified_level)) {
+ // Found both.
+ *j = b;
+ break;
+ }
+ }
+ return 1;
+}
+
+
+unsigned int create_empty_block(metadata_t * m) {
+ blockdata_t *i,*j;
+ if(!identify_compatible_block_pair(m, &i, &j)){
+ // Nothing to do unless there is a compatible block pair
+ // to merge.
+ return 0;
+ }
+ return merge_blocks(m,i,j);
+}
+
// Shift the current block.
unsigned int shift_current_block(metadata_t * m) {
if(!occupy_available_empty_block(m)) {
@@ -116,6 +234,8 @@
// ----------------------------------------------------------------------------
// Implementation of the interface functions (specified in median.h).
+
+// Suggest the size of the buffer needed for a fixed epsilon and maxN.
median_error_t median_suggest_buffer_size(double epsilon, size_t maxN, size_t *suggested_size){
// First check for sane parameters.
@@ -131,11 +251,21 @@
metadata_t m;
m.nLevels = calculate_nLevels(maxN);
m.nMembers = calculate_nMembers(epsilon);
- *suggested_size = buffersize(&m);
+
+ // The size is the size of the buffer and the spare needed for merging
+ // and outputing. If we have many ongoing buffers, we can do with a single
+ // spare space buffer. We can figure out that optimization later.
+ // Ideally, this will be done by keeping a pointer to the global spare space
+ // within the metadata_t block. I prefer keeping this data structure
+ // relocatable and serializable. So we may need to think about what the
+ // alternatives are.
+ *suggested_size = buffersize(&m)+sparespace(&m);
// Things worked. Return MEDIAN_OK
return MEDIAN_OK;
}
+
+// Initialize an allocated buffer.
median_error_t median_init_buffer(void * buffer, size_t buffer_size, double epsilon, size_t maxN, median_buffer_t *initialized_buffer){
// Initialize.
@@ -153,6 +283,7 @@
m->nMembers = calculate_nMembers(epsilon);
m->nLevels = calculate_nLevels(maxN);
m->currentBufferIdx = 0;
+ m->spareSize = buffer_size - buffersize(m);
// Zero all the data following the metadata block.
// Strictly this should not be necessary, but I'm a coward!
bzero(m->data, buffersize(m) - sizeof(metadata_t));
@@ -221,7 +352,7 @@
// First print out all the metadata.
metadata_t * m = (metadata_t *) buffer;
blockdata_t * current = get_current_block(m);
- fprintf(stderr, "Metadata:\n Next GID:%d\n nMembers:%d\n nLevels:%d\n CurrentBlock:%d\n",m->gid,(unsigned)m->nMembers,(unsigned)m->nLevels, current->id);
+ fprintf(stderr, "Metadata:\n Next GID:%d\n nMembers:%d\n nLevels:%d\n CurrentBlock:%d\n SpareSize:%d\n",m->gid,(unsigned)m->nMembers,(unsigned)m->nLevels, current->id,(unsigned)m->spareSize);
// Now dump the blocks.
for(unsigned char * ptr = (unsigned char *) m->data; // Start of the data blocks.
diff --git a/median.main.c b/median.main.c
index 1aef5c7..49dac5d 100644
--- a/median.main.c
+++ b/median.main.c
@@ -3,6 +3,7 @@
#include "median.h"
#include "hex.h"
+#define TEST_SIZE 1024*1024*128 // 128M
// A sinple main routine meant as an example,
// and also to unit test most of the intersting
// functions of the median module.
@@ -10,16 +11,16 @@
// Call suggest buffer size to determine the size of the buffer
// we need to build the data structure.
size_t n = 0;
- assert(median_suggest_buffer_size(.001, 1000, &n) == MEDIAN_OK);
+ assert(median_suggest_buffer_size(.001, TEST_SIZE , &n) == MEDIAN_OK);
// Allocate the buffer of the required size. And then
// initialize it (median_init_buffer).
void * b = malloc(n);
median_buffer_t buf;
- assert(median_init_buffer(b, n, .001, 1000, &buf) == MEDIAN_OK);
+ assert(median_init_buffer(b, n, .001, TEST_SIZE, &buf) == MEDIAN_OK);
// Insert some data.
- for(median_data_t i = 1; i < 3010; i++) {
+ for(median_data_t i = 1; i < TEST_SIZE; i++) { // 1G
assert(median_insert_data(buf,i) == MEDIAN_OK);
}
