ubgpsuite/lonetix/bgp/bytebuf.c

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2021-06-07 16:55:13 +02:00
// SPDX-License-Identifier: LGPL-3.0-or-later
/**
* \file bgp/bytebuf.c
*
* Trivial BGP memory allocator for basic BGP workloads.
*
* \copyright The DoubleFourteen Code Forge (C) All Rights Reserved
* \author Lorenzo Cogotti
*/
#include "bgp/bytebuf.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
STATIC_ASSERT(BGP_MEMBUF_ALIGN >= 4, "bytebuf.c assumes Uint32 header");
#define USEDBIT BIT(0)
#define MAXBUFCHUNKSIZ 0xffffffffuLL
#define BLKSIZ(ptr) ((*(Uint32 *) (ptr)) & ~USEDBIT)
#define ISUSED(ptr) (((*(Uint32 *) (ptr)) & USEDBIT) != 0)
#define SETUSED(ptr) ((void) ((*(Uint32 *) (ptr)) |= USEDBIT))
#define CLRUSED(ptr) ((void) ((*(Uint32 *) (ptr)) &= ~USEDBIT))
static Boolean Mem_IsInBuffer(Bgpbytebuf *buf, void *ptr)
{
return (Uint8 *) ptr >= buf->base &&
(Uint8 *) ptr < buf->base + buf->size;
}
static Uint8 *Mem_FindPrevChunk(Bgpbytebuf *buf, void *chunk)
{
assert(Mem_IsInBuffer(buf, chunk));
Uint8 *p = buf->base;
while (p < (Uint8 *) chunk) {
size_t siz = BLKSIZ(p);
if (p + siz == (Uint8 *) chunk)
return p;
p += siz;
}
return NULL;
}
static void Mem_BgpFree(void *allocator, void *ptr)
{
Bgpbytebuf *buf = (Bgpbytebuf *) allocator;
// Regular free() for out of buffer allocations
if (!Mem_IsInBuffer(buf, ptr)) {
free(ptr);
return;
}
// Get pointer to chunk
Uint8 *p = (Uint8 *) ptr - 4;
assert(ISUSED(p));
// Get buffer limit
Uint8 *lim = buf->base + buf->pos;
Uint32 siz = BLKSIZ(p);
CLRUSED(p); // toggle off USEDBIT
// Find successor if any
Uint8 *next = p + siz;
if (next < lim && !ISUSED(next)) {
// Merge forward
siz += BLKSIZ(next);
*(Uint32 *) p = siz;
}
// Find predecessor, if any
Uint8 *prev = Mem_FindPrevChunk(buf, p);
if (prev && !ISUSED(prev)) {
// Merge backwards
siz += BLKSIZ(prev);
p = prev;
*(Uint32 *) p = siz;
}
// Move position backwards when freeing last block
if (p + siz == lim)
buf->pos -= siz;
}
static void *Mem_BgpDoRealloc(Bgpbytebuf *buf, void *oldp, size_t nbytes)
{
// Use plain realloc() if we're not managing a buffered pointer
if (!Mem_IsInBuffer(buf, oldp))
return realloc(oldp, nbytes);
assert(IS_PTR_ALIGNED(oldp, BGP_MEMBUF_ALIGN));
Uint8 *ptr = (Uint8 *) oldp - 4;
assert(ISUSED(ptr));
Uint32 oldSiz = BLKSIZ(ptr);
assert(buf->pos >= oldSiz);
size_t siz = 4 + ALIGN(nbytes, BGP_MEMBUF_ALIGN);
if (oldSiz >= siz) {
// Shrink operation, free up the trailing part if we're the last chunk
if (ptr + oldSiz == buf->base + buf->pos) {
*(Uint32 *) ptr = siz | USEDBIT;
buf->pos -= (oldSiz - siz);
}
return oldp;
}
// May only grow a chunk if this is the last one and we don't overflow
if (ptr + oldSiz != buf->base + buf->pos)
return NULL;
size_t newPos = buf->pos + (siz - oldSiz);
if (newPos > buf->size)
return NULL;
// Ok to grow the chunk
*(Uint32 *) ptr = siz | USEDBIT;
buf->pos = newPos;
return oldp;
}
static void *Mem_BgpDoAlloc(Bgpbytebuf *buf, size_t nbytes)
{
// Use plain malloc() for large allocations or when out of buffer space
size_t siz = 4 + ALIGN(nbytes, BGP_MEMBUF_ALIGN);
if (buf->pos + siz > buf->size || siz > MAXBUFCHUNKSIZ)
return malloc(nbytes);
// Return the next chunk available
Uint32 *ptr = (Uint32 *) (buf->base + buf->pos);
buf->pos += siz;
assert((siz & USEDBIT) == 0);
*ptr++ = siz | USEDBIT;
return ptr;
}
static void *Mem_BgpAlloc(void *allocator, size_t nbytes, void *oldp)
{
Bgpbytebuf *buf = (Bgpbytebuf *) allocator;
// Handle common allocations with no `oldp`
if (!oldp)
return Mem_BgpDoAlloc(buf, nbytes);
// Attempt memory reuse
void *ptr = Mem_BgpDoRealloc(buf, oldp, nbytes);
if (ptr)
return ptr;
// Fallback to simple allocation+memcpy()
ptr = Mem_BgpDoAlloc(buf, nbytes);
if (ptr) {
memcpy(ptr, oldp, nbytes);
Mem_BgpFree(buf, oldp);
}
return ptr;
}
static const MemOps mem_bgpBufTable = {
Mem_BgpAlloc,
Mem_BgpFree
};
const MemOps *const Mem_BgpBufOps = &mem_bgpBufTable;