Function Fresnel_int, x, sine = sin, complementary = comp

;+
; NAME:
;		FRESNEL_INT
; VERSION:
;		4.0
; PURPOSE:
;		Calculates the Fresnel Integrals, C(x) or S(X).
; CATEGORY:
;		Mathematical function (general).
; CALLING SEQUENCE:
;		Result = FRESNEL_INT (X [, keywords])
; INPUTS:
;	X
;		Numeric, otherwise arbitrary.
; OPTIONAL INPUT PARAMETERS:
;		None.
; KEYWORD PARAMETERS:
;	/SINE
;		Switch.  If set, the Fresnel sine integral, S(X), is returned.
;	/COMPLEMENTARY
;		Switch.  If set, 1/2 - C(X) (or S(X)) is returned.
; OUTPUTS:
;		Returns the Fresnel Cosine integral C(X) or, if /COMPLEMENTARY is set,
;		the sine integral S(X).  If /COMPLEMENTARY is set, the output is
;		1/2 (the value at infinity) - C(X) (or S(X)).
; OPTIONAL OUTPUT PARAMETERS:
;		None.
; COMMON BLOCKS:
;		None.
; SIDE EFFECTS:
;		None.
; RESTRICTIONS:
;		While the function is defined also for complex values of X, large
;		complex values may cause calculational instabilities.  A warning is
;		issued in this case.
; PROCEDURE:
;		Uses the function ERRORF_MM from MIDL, as well as CAST and TYPE, also
;		from MIDL.
; MODIFICATION HISTORY:
;		Created 20-MAR-1996 by Mati Meron.
;		Checked for operation under Windows, 25-JAN-2001, by Mati Meron.
;-

	on_error, 1
	typ = Type(x)
	cof = 2*sqrt(!dpi)
	opi = 0.25d*dcomplex(1, 1)
	oni = 0.25d*dcomplex(1,-1)

	if keyword_set(sin) $
		then res = oni*Errorf_mm(cof*oni*x, comp = comp) + $
			opi*Errorf_mm(cof*opi*x, comp = comp) $
		else res = opi*Errorf_mm(cof*oni*x, comp = comp) + $
			oni*Errorf_mm(cof*opi*x, comp = comp)

	return, Cast(res,4,typ,/fix)
end