shithub: mc

ref: 0dd5d1f71505ce3d8a51e8244cf3128c54eb8293
dir: /lib/std/varargs.myr/

use "types.use"
use "introspect.use"
use "sleq.use"
use "die.use"

pkg std =
	type valist

	const vastart	: (args : ...# -> valist)
	const vatype	: (ap : valist# -> byte[:])
	const vabytes	: (ap : valist# -> byte[:])
	const vaenter	: (ap : valist# -> valist)
	generic vanext	: (ap : valist# -> @a)
;;

type valist = struct
	args	: byte#
	tc	: typecursor
;;

/* 
 * a valist is really just a pointer to the varargs.
 * we assume that these sit on the stack nicely,
 * and don't need special handling to get to.
 * 
 * This will be a problem when we switch to a
 * register based convention. We might want to
 * force varargs onto the stack regardless.
 */
const vastart = {args
	var tc, a, ip

	/*
	pull out the args. These are on the stacks like so:

		[ required ]
		[   args   ]
	       ---variadic--- 
		[ typeinfo ] --> type description
	        ------------
		[ variadic ]
		[   args   ]
		[   here   ]

	&args points to the typeinfo, &args + sizeof(void#)
	points to the rest argument.
	*/
		
	tc = typeenc(args)
	ip = (args castto(intptr)) + sizeof(byte#)
	a = ip castto(byte#)
	-> [.args = a, .tc = tc]
}

const vaenter = {ap
	match typedesc(vatype(ap))
	| `Tyslice enc:	-> [.args=sliceptr(ap.args), .tc=[.nelt=slicelen(ap.args), .rem=enc, .isiter=false]]
	| `Tytuple tc:	-> [.args=ap.args, .tc=tc]
	| `Tystruct tc:	-> [.args=ap.args, .tc=tc]
	| `Tyunion tc:	-> [.args=addp(ap.args, 4), .tc=tc]
	| `Tyarray (sz, enc):	-> [.args=ap.args, .tc=[.nelt=sz, .rem=enc, .isiter=false]]
	| `Tyname (name, enc):	-> [.args=ap.args, .tc=typeenccursor(enc)]
	| _:	std.die("unable to enter type")
	;;
}

const vatype = {ap
	-> tcpeek(&ap.tc)
}

const vabytes = {ap
	var sl
	var ti, align, sz
	var p

	ti = typeinfo(tcpeek(&ap.tc))

	/* apply the alignment to the arg pointer */
	align = ti.align castto(intptr)
	p = ap.args castto(intptr)
	p = (p + align - 1) & ~(align - 1)
	ap.args = p castto(byte#)

	sl = ap.args[:ti.size]
	tcnext(&ap.tc)

	sz = ti.size castto(intptr)
	ap.args = ((p castto(intptr)) + sz) castto(byte#)

	-> sl
}

generic vanext = {ap -> @a
	var ti
	var align
	var p

	ti = typeinfo(tcpeek(&ap.tc))

	/* apply the alignment to the arg pointer */
	align = ti.align castto(intptr)
	p = ap.args castto(intptr)
	p = (p + align - 1) & ~(align - 1)

	/* TODO: check for type mismatch */
	tcnext(&ap.tc)
	/* only move on after we read through the value */
	ap.args = ((p castto(intptr)) + sizeof(@a)) castto(byte#)
	-> (p castto(@a#))#
}

const addp = {p, k
	-> (p castto(intptr)) + k castto(byte#)
}

const sliceptr = {p
	-> (p castto(byte##))#
}

const slicelen = {p
	p = addp(p, sizeof(intptr))
	-> (p castto(size#))#
}