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use "die"
use "extremum"
use "memops"
use "syswrap"
use "threadhooks"
use "types"
use "units"

pkg std =
	/* null pointers. only used internally. */
	pkglocal const Zsliceptr	= (0 : byte#)
	pkglocal const Align	= 16	/* minimum allocation alignment */

	pkglocal const align	: (m : std.size, align : std.size -> std.size)
	pkglocal const allocsz	: (sz : std.size -> std.size)

	pkglocal const bytealloc	: (sz:size	-> byte#)
	pkglocal const zbytealloc	: (sz:size	-> byte#)
	pkglocal const bytefree	: (m:byte#, sz:size	-> void)
;;

const Zslab	= (0 : slab#)
const Zchunk	= (0 : chunk#)
const Slabsz 	= 1*MiB	/* 1 meg slabs */
const Cachemax	= 16	/* maximum number of slabs in the cache */
const Bktmax	= 32*KiB	/* Slabsz / 8; a balance. */
const Pagesz	= 4*KiB

var buckets	: bucket[32] /* excessive */

type bucket = struct
	sz	: size	/* aligned size */
	nper	: size	/* max number of elements per slab */
	slabs	: slab#	/* partially filled or free slabs */
	cache	: slab# /* cache of empty slabs, to prevent thrashing */
	ncache	: size  /* size of cache */
;;

type slab = struct
	head	: byte#	/* head of virtual addresses, so we don't leak address space */
	next	: slab#	/* the next slab on the chain */
	freehd	: chunk#	/* the nodes we're allocating */
	nfree	: size	/* the number of free nodes */
;;

type chunk = struct	/* NB: must be smaller than sizeof(slab) */
	next	: chunk#	/* the next chunk in the free list */
;;

const __init__ = {
	for var i = 0; i < buckets.len && (Align << i) <= Bktmax; i++
		bktinit(&buckets[i], Align << i)
	;;
}

const zbytealloc = {sz
	var p

	p = bytealloc(sz)
	memfill(p, 0, sz)
	-> p
}

/* Allocates a blob that is 'sz' bytes long. Dies if the allocation fails */
const bytealloc = {sz
	var bkt, p

	if (sz <= Bktmax)
		bkt = &buckets[bktnum(sz)]
		lock(memlck)
		p = bktalloc(bkt)
		unlock(memlck)
	else
		p = getmem(sz)
		if p == Failmem
			die("could not get memory\n")
		;;
	;;
	-> p
}

/* frees a blob that is 'sz' bytes long. */
const bytefree = {p, sz
	var bkt

	memfill(p, 0xa8, sz)
	if (sz < Bktmax)
		bkt = &buckets[bktnum(sz)]
		lock(memlck)
		bktfree(bkt, p)
		unlock(memlck)
	else
		freemem(p, sz)
	;;
}

/* Sets up a single empty bucket */
const bktinit = {b, sz
	b.sz = align(sz, Align)
	b.nper = (Slabsz - sizeof(slab))/b.sz
	b.slabs = Zslab
	b.cache = Zslab
	b.ncache = 0
}

/* Creates a slab for bucket 'bkt', and fills the chunk list */
const mkslab = {bkt
	var p, s
	var b, bnext
	var off /* offset of chunk head */

	if bkt.ncache > 0
		s = bkt.cache
		bkt.cache = s.next
		bkt.ncache--
	;;
	/*
	tricky: we need power of two alignment, so we allocate double the
	needed size, chop off the unaligned ends, and waste the address
	space. Since the OS is "smart enough", this shouldn't actually
	cost us memory, and 64 bits of address space means that we're not
	going to have issues with running out of address space for a
	while. On a 32 bit system this would be a bad idea.
	*/
	p = getmem(Slabsz*2)
	if p == Failmem
		die("Unable to get memory")
	;;

	s = (align((p : size), Slabsz) : slab#)
	s.head = p
	s.nfree = bkt.nper
	/* skip past the slab header */
	off = align(sizeof(slab), Align)
	bnext = nextchunk((s : chunk#), off)
	s.freehd = bnext
	for var i = 0; i < bkt.nper; i++
		b = bnext
		bnext = nextchunk(b, bkt.sz)
		b.next = bnext
	;;
	b.next = Zchunk
	-> s
}

/* 
Allocates a node from bucket 'bkt', crashing if the
allocation cannot be satisfied. Will create a new slab
if there are no slabs on the freelist.
*/
const bktalloc = {bkt
	var s
	var b

	/* find a slab */
	s = bkt.slabs
	if s == Zslab
		s = mkslab(bkt)
		if s == Zslab
			die("No memory left")
		;;
		bkt.slabs = s
	;;

	/* grab the first chunk on the slab */
	b = s.freehd
	s.freehd = b.next
	s.nfree--
	if s.nfree == 0
		bkt.slabs = s.next
		s.next = Zslab
	;;

	-> (b : byte#)
}

/*
Frees a chunk of memory 'm' into bucket 'bkt'.
Assumes that the memory already came from a slab
that was created for bucket 'bkt'. Will crash
if this is not the case.
*/
const bktfree = {bkt, m
	var s, b

	s = (mtrunc(m, Slabsz) : slab#)
	b = (m : chunk#)
	if s.nfree == 0
		s.next = bkt.slabs
		bkt.slabs = s
	elif s.nfree == bkt.nper
		/*
		HACK HACK HACK: if we can't unmap, keep an infinite cache per slab size.
		We should solve this better somehow.
		*/
		if bkt.ncache < Cachemax || !Canunmap
			s.next = bkt.cache
			bkt.cache = s
		else
			/* we mapped 2*Slabsz so we could align it,
			 so we need to unmap the same */
			freemem(s.head, Slabsz*2)
		;;
	;;
	s.nfree++
	b.next = s.freehd
	s.freehd = b
}

/*
Finds the correct bucket index to allocate from
for allocations of size 'sz'
*/
const bktnum = {sz
	var bktsz

	bktsz = Align
	for var i = 0; bktsz <= Bktmax; i++
		if bktsz >= sz
			-> i
		;;
		bktsz *= 2
	;;
	die("Size does not match any buckets")
}

/*
returns the actual size we allocated for a given
size request
*/
const allocsz = {sz
	var bktsz

	if sz <= Bktmax
		bktsz = Align
		for var i = 0; bktsz <= Bktmax; i++
			if bktsz >= sz
				-> bktsz
			;;
			bktsz *= 2
		;;
	else
		-> align(sz, Pagesz)
	;;
	die("Size does not match any buckets")
}

/*
aligns a size to a requested alignment.
'align' must be a power of two
*/
const align = {v, align
	-> (v + align - 1) & ~(align - 1)
}

/*
chunks are variable sizes, so we can't just
index to get to the next one
*/
const nextchunk = {b, sz : size
	-> ((b : intptr) + (sz : intptr) : chunk#)
}

/*
truncates a pointer to 'align'. 'align' must
be a power of two.
*/
const mtrunc = {m, align
	-> ((m : intptr) & ~((align : intptr) - 1) : byte#)
}