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;;; Chickadee Game Toolkit
;;; Copyright © 2016 David Thompson <davet@gnu.org>
;;;
;;; Chickadee is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published
;;; by the Free Software Foundation, either version 3 of the License,
;;; or (at your option) any later version.
;;;
;;; Chickadee is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
(define-module (chickadee math)
#:export (pi
pi/2
tau
cotan
clamp
min
max
lerp
degrees->radians
radians->degrees)
#:replace (min max))
(define pi 3.1415926535897932)
(define pi/2 1.5707963267948966)
(define tau 6.283185307179586) ;; AKA 2pi
(define-inlinable (cotan z)
"Return the cotangent of Z."
(/ 1.0 (tan z)))
(define-inlinable (clamp min max x)
"Restrict X to the range defined by MIN and MAX. Assumes that MIN is
actually less than MAX."
(cond ((< x min) min)
((> x max) max)
(else x)))
;; Some macro trickery to inline calls to min/max with 2 arguments.
;; We often call min/max on floating point values, so inlining such
;; calls allows the compiler to unbox many of these operations,
;; reducing allocation.
(define-syntax min
(syntax-rules ()
((_ a b)
(if (< a b) a b))
((_ a b ...)
(let ((m (min b ...)))
(if (< a m) a m)))))
(define-syntax max
(syntax-rules ()
((_ a b) (if (> a b) a b))
((_ a b ...)
(let ((m (max b ...)))
(if (> a m) a m)))))
(define-inlinable (lerp start end alpha)
(+ (* start (- 1.0 alpha))
(* end alpha)))
(define-inlinable (degrees->radians degrees)
(/ (* pi degrees) 180.0))
(define-inlinable (radians->degrees radians)
(/ (* 180.0 radians) pi))
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