shithub: mc

ref: 69d83a1be81a97e50f1b83a2cf327f96064f1152
dir: /lib/math/scale2-impl.myr/

use std

use "fpmath"
use "util"

/*
   The scaleB function recommended by the 2008 revision of IEEE
   754. Since only integer exponents are considered, the naive
   approach works quite well.
 */
pkg math =
	const scale232 : (x : flt32, m : int32 -> flt32)
	const scale264 : (x : flt64, m : int64 -> flt64)
;;

const scale232 = {x : flt32, m : int32
	var n, e, s
	(n, e, s) = std.flt32explode(x)
	(n, e, s) = scale2gen(n, e, s, -126, 127, 24, m)
	-> std.flt32assem(n, e, s)
}

const scale264 = {x : flt64, m : int64
	var n, e, s
	(n, e, s) = std.flt64explode(x)
	(n, e, s) = scale2gen(n, e, s, -1022, 1023, 53, m)
	-> std.flt64assem(n, e, s)
}

generic scale2gen = {n : bool, e : @i, s : @u, emin : @i, emax : @i, p : @u, m : @i :: numeric, integral @i, numeric, integral @u
	if e < emin && s == 0
		-> (n, e, s)
	elif m == 0
		-> (n, e, s)
	elif m < 0
		var sprime = s
		var eprime = e
		if e < emin
			sprime = s >> (-m)
			if need_round_away(0, (s : uint64), (-m : int64))
				sprime++
			;;
			eprime = emin - 1
		elif e + m < emin - p - 2
			sprime = 0
			eprime = emin - 1
		elif e + m < emin
			sprime = s >> ((emin - m - e) : @u)
			if need_round_away(0, (s : uint64), ((emin - m - e) : int64))
				sprime++
			;;
			eprime = emin - 1
		else
			eprime = e + m
		;;
		-> (n, eprime, sprime)
	;;

	if e < emin
		var first_1 = find_first1_64((s : uint64), (p : int64))
		var shift = p - (first_1 : @u) - 1
		if m >= (shift : @i)
			s = s << shift
			m -= (shift : @i)
			e = emin
		else
			-> (n, e, s << m)
		;;
	;;

	if e + m > emax && s != 0
		-> (n, emax + 1, 1 << (p - 1))
	;;

	-> (n, e + m, s)
}