Buddy Memorry

#include "buddy.h"
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>
#include <string.h>

#define NODE_UNUSED 0
#define NODE_USED 1    
#define NODE_SPLIT 2
#define NODE_FULL 3

struct buddy {
    int level;
    uint8_t tree[1];
};

struct buddy * 
buddy_new(int level) {
    int size = 1 << level;
    struct buddy * self = malloc(sizeof(struct buddy) + sizeof(uint8_t) * (size * 2 - 2));
    self->level = level;
    memset(self->tree , NODE_UNUSED , size*2-1);
    return self;
}

void
buddy_delete(struct buddy * self) {
    free(self);
}

static inline int
is_pow_of_2(uint32_t x) {
    return !(x & (x-1));
}

static inline uint32_t
next_pow_of_2(uint32_t x) {
    if ( is_pow_of_2(x) )
        return x;
    x |= x>>1;
    x |= x>>2;
    x |= x>>4;
    x |= x>>8;
    x |= x>>16;
    return x+1;
}

static inline int
_index_offset(int index, int level, int max_level) {
    return ((index + 1) - (1 << level)) << (max_level - level);
}

static void 
_mark_parent(struct buddy * self, int index) {
    for (;;) {
        int buddy = index - 1 + (index & 1) * 2;
        if (buddy > 0 && (self->tree[buddy] == NODE_USED ||    self->tree[buddy] == NODE_FULL)) {
            index = (index + 1) / 2 - 1;
            self->tree[index] = NODE_FULL;
        } else {
            return;
        }
    }
}

int 
buddy_alloc(struct buddy * self , int s) {
    int size;
    if (s==0) {
        size = 1;
    } else {
        size = (int)next_pow_of_2(s);
    }
    int length = 1 << self->level;

    if (size > length)
        return -1;

    int index = 0;
    int level = 0;

    while (index >= 0) {
        if (size == length) {
            if (self->tree[index] == NODE_UNUSED) {
                self->tree[index] = NODE_USED;
                _mark_parent(self, index);
                return _index_offset(index, level, self->level);
            }
        } else {
            // size < length
            switch (self->tree[index]) {
            case NODE_USED:
            case NODE_FULL:
                break;
            case NODE_UNUSED:
                // split first
                self->tree[index] = NODE_SPLIT;
                self->tree[index*2+1] = NODE_UNUSED;
                self->tree[index*2+2] = NODE_UNUSED;
            default:
                index = index * 2 + 1;
                length /= 2;
                level++;
                continue;
            }
        }
        if (index & 1) {
            ++index;
            continue;
        }
        for (;;) {
            level--;
            length *= 2;
            index = (index+1)/2 -1;
            if (index < 0)
                return -1;
            if (index & 1) {
                ++index;
                break;
            }
        }
    }

    return -1;
}

static void 
_combine(struct buddy * self, int index) {
    for (;;) {
        int buddy = index - 1 + (index & 1) * 2;
        if (buddy < 0 || self->tree[buddy] != NODE_UNUSED) {
            self->tree[index] = NODE_UNUSED;
            while (((index = (index + 1) / 2 - 1) >= 0) &&  self->tree[index] == NODE_FULL){
                self->tree[index] = NODE_SPLIT;
            }
            return;
        }
        index = (index + 1) / 2 - 1;
    }
}

void
buddy_free(struct buddy * self, int offset) {
    assert( offset < (1<< self->level));
    int left = 0;
    int length = 1 << self->level;
    int index = 0;

    for (;;) {
        switch (self->tree[index]) {
        case NODE_USED:
            assert(offset == left);
            _combine(self, index);
            return;
        case NODE_UNUSED:
            assert(0);
            return;
        default:
            length /= 2;
            if (offset < left + length) {
                index = index * 2 + 1;
            } else {
                left += length;
                index = index * 2 + 2;
            }
            break;
        }
    }
}

int
buddy_size(struct buddy * self, int offset) {
    assert( offset < (1<< self->level));
    int left = 0;
    int length = 1 << self->level;
    int index = 0;

    for (;;) {
        switch (self->tree[index]) {
        case NODE_USED:
            assert(offset == left);
            return length;
        case NODE_UNUSED:
            assert(0);
            return length;
        default:
            length /= 2;
            if (offset < left + length) {
                index = index * 2 + 1;
            } else {
                left += length;
                index = index * 2 + 2;
            }
            break;
        }
    }
}

static void
_dump(struct buddy * self, int index , int level) {
    switch (self->tree[index]) {
    case NODE_UNUSED:
        printf("(%d:%d)", _index_offset(index, level, self->level) , 1 << (self->level - level));
        break;
    case NODE_USED:
        printf("[%d:%d]", _index_offset(index, level, self->level) , 1 << (self->level - level));
        break;
    case NODE_FULL:
        printf("{");
        _dump(self, index * 2 + 1 , level+1);
        _dump(self, index * 2 + 2 , level+1);
        printf("}");
        break;
    default:
        printf("(");
        _dump(self, index * 2 + 1 , level+1);
        _dump(self, index * 2 + 2 , level+1);
        printf(")");
        break;
    }
}

void
buddy_dump(struct buddy * self) {
    _dump(self, 0 , 0);
    printf("\n");
}