/* -*- mode: C; c-basic-offset: 4 -*- */
#ident "Copyright (c) 2009 Tokutek Inc.  All rights reserved."
#ident "The technology is licensed by the Massachusetts Institute of Technology, Rutgers State University of New Jersey, and the Research Foundation of State University of New York at Stony Brook under United States of America Serial No. 11/760379 and to the patents and/or patent applications resulting from it."
#ident "$Id$"

#include "includes.h"

// Here's a very simple implementation.
// It's not very fast at allocating or freeing.


struct blockpair {
    u_int64_t offset;
    u_int64_t size;
};

struct block_allocator {
    u_int64_t reserve_at_beginning; // How much to reserve at the beginning
    u_int64_t alignment;            // Block alignment
    u_int64_t n_blocks; // How many blocks
    u_int64_t blocks_array_size; // How big is the blocks_array.  Must be >= n_blocks.
    struct blockpair *blocks_array; // These blocks are sorted by address.
    u_int64_t next_fit_counter; // Used for the next_fit algorithm.
};

void
block_allocator_validate (BLOCK_ALLOCATOR ba) {
    u_int64_t i;
    for (i=0; i<ba->n_blocks; i++) {
	if (i>0) {
	    assert(ba->blocks_array[i].offset >  ba->blocks_array[i-1].offset);
	    assert(ba->blocks_array[i].offset >= ba->blocks_array[i-1].offset + ba->blocks_array[i-1].size );
	}
    }
}

#if 0
#define VALIDATE(b) block_allocator_validate(b)
#else
#define VALIDATE(b) ((void)0)
#endif

#if 0
void
block_allocator_print (BLOCK_ALLOCATOR ba) {
    u_int64_t i;
    for (i=0; i<ba->n_blocks; i++) {
	printf("%" PRId64 ":%" PRId64 " ", ba->blocks_array[i].offset, ba->blocks_array[i].size);
    }
    printf("\n");
    VALIDATE(ba);
}
#endif

void
create_block_allocator (BLOCK_ALLOCATOR *ba, u_int64_t reserve_at_beginning, u_int64_t alignment) {
    BLOCK_ALLOCATOR XMALLOC(result);
    result->reserve_at_beginning = reserve_at_beginning;
    result->alignment = alignment;
    result->n_blocks = 0;
    result->blocks_array_size = 1;
    XMALLOC_N(result->blocks_array_size, result->blocks_array);
    result->next_fit_counter = 0;
    *ba = result;
    VALIDATE(result);
}

void
destroy_block_allocator (BLOCK_ALLOCATOR *bap) {
    BLOCK_ALLOCATOR ba = *bap;
    *bap = 0;
    toku_free(ba->blocks_array);
    toku_free(ba);
}

static void
grow_blocks_array (BLOCK_ALLOCATOR ba) {
    if (ba->n_blocks >= ba->blocks_array_size) {
	ba->blocks_array_size *= 2;
	XREALLOC_N(ba->blocks_array_size, ba->blocks_array);
    }
}

void
block_allocator_alloc_block_at (BLOCK_ALLOCATOR ba, u_int64_t size, u_int64_t offset) {
    assert(offset%ba->alignment == 0);
    u_int64_t i;
    VALIDATE(ba);
    assert(offset >= ba->reserve_at_beginning);
    grow_blocks_array(ba);
    // Just do a linear search for the block
    for (i=0; i<ba->n_blocks; i++) {
	if (ba->blocks_array[i].offset > offset) {
	    // allocate it in that slot
	    // Don't do error checking, since we require that the blocks don't overlap.
	    // Slide everything over
	    memmove(ba->blocks_array+i+1, ba->blocks_array+i, (ba->n_blocks - i)*sizeof(struct blockpair));
	    ba->blocks_array[i].offset = offset;
	    ba->blocks_array[i].size   = size;
	    ba->n_blocks++;
	    VALIDATE(ba);
	    return;
	}
    }
    // Goes at the end
    ba->blocks_array[ba->n_blocks].offset = offset;
    ba->blocks_array[ba->n_blocks].size   = size;
    ba->n_blocks++;
    VALIDATE(ba);
}

static inline u_int64_t
align (u_int64_t value, BLOCK_ALLOCATOR ba) {
    return ((value+ba->alignment-1)/ba->alignment)*ba->alignment;
}

void
block_allocator_alloc_block (BLOCK_ALLOCATOR ba, u_int64_t size, u_int64_t *offset) {
    grow_blocks_array(ba);
    if (ba->n_blocks==0) {
	ba->blocks_array[0].offset = ba->reserve_at_beginning;
	ba->blocks_array[0].size  = size;
	*offset = ba->reserve_at_beginning;
	ba->n_blocks++;
	return;
    }
    u_int64_t i;
    u_int64_t blocknum = ba->next_fit_counter;
    // Implement next fit.
    for (i=0; i<ba->n_blocks; i++, blocknum++) {
	if (blocknum>=ba->n_blocks) blocknum=0;
	// Consider the space after blocknum
	if (blocknum+1 == ba->n_blocks) continue; // Can't use the space after the last block, since that would be new space.
	struct blockpair *bp = &ba->blocks_array[blocknum];
	u_int64_t this_offset = bp[0].offset;
	u_int64_t this_size   = bp[0].size;
	u_int64_t answer_offset = align(this_offset + this_size, ba);
	if (answer_offset + size > bp[1].offset) continue; // The block we want doesn't fit after this block.
	// It fits, so allocate it here.
	memmove(bp+2, bp+1, (ba->n_blocks - blocknum -1)*sizeof(struct blockpair));
	bp[1].offset = answer_offset;
	bp[1].size   = size;
	ba->n_blocks++;
	ba->next_fit_counter = blocknum;
	*offset = answer_offset;
	VALIDATE(ba);
	return;
    }
    // It didn't fit anywhere, so fit it on the end.
    struct blockpair *bp = &ba->blocks_array[ba->n_blocks];
    u_int64_t answer_offset = align(bp[-1].offset+bp[-1].size, ba);
    bp->offset = answer_offset;
    bp->size   = size;
    ba->n_blocks++;
    *offset = answer_offset;
    VALIDATE(ba);
}

static int64_t
find_block (BLOCK_ALLOCATOR ba, u_int64_t offset)
// Find the index in the blocks array that has a particular offset.  Requires that the block exist.
// Use binary search so it runs fast.
{
    VALIDATE(ba);
    if (ba->n_blocks==1) {
	assert(ba->blocks_array[0].offset == offset);
	return 0;
    }
    u_int64_t lo = 0;
    u_int64_t hi = ba->n_blocks;
    while (1) {
	assert(lo<hi); // otherwise no such block exists.
	u_int64_t mid = (lo+hi)/2;
	u_int64_t thisoff = ba->blocks_array[mid].offset;
	//printf("lo=%" PRId64 " hi=%" PRId64 " mid=%" PRId64 "  thisoff=%" PRId64 " offset=%" PRId64 "\n", lo, hi, mid, thisoff, offset);
	if (thisoff < offset) {
	    lo = mid+1;
	} else if (thisoff > offset) {
	    hi = mid;
	} else {
	    return mid;
	}
    }
}

void
block_allocator_free_block (BLOCK_ALLOCATOR ba, u_int64_t offset) {
    VALIDATE(ba);
    int64_t bn = find_block(ba, offset);
    assert(bn>=0); // we require that there is a block with that offset.  Might as well abort if no such block exists.
    memmove(&ba->blocks_array[bn], &ba->blocks_array[bn+1], (ba->n_blocks-bn-1) * sizeof(struct blockpair));
    ba->n_blocks--;
    VALIDATE(ba);
}

u_int64_t
block_allocator_block_size (BLOCK_ALLOCATOR ba, u_int64_t offset) {
    int64_t bn = find_block(ba, offset);
    assert(bn>=0); // we require that there is a block with that offset.  Might as well abort if no such block exists.
    return ba->blocks_array[bn].size;
}

u_int64_t
block_allocator_allocated_limit (BLOCK_ALLOCATOR ba) {
    if (ba->n_blocks==0) return ba->reserve_at_beginning;
    else {
	struct blockpair *last = &ba->blocks_array[ba->n_blocks-1];
	return last->offset + last->size;
    }
}
