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;;; Chickadee Game Toolkit
;;; Copyright © 2016 David Thompson <dthompson2@worcester.edu>
;;;
;;; Licensed under the Apache License, Version 2.0 (the "License");
;;; you may not use this file except in compliance with the License.
;;; You may obtain a copy of the License at
;;;
;;; http://www.apache.org/licenses/LICENSE-2.0
;;;
;;; Unless required by applicable law or agreed to in writing, software
;;; distributed under the License is distributed on an "AS IS" BASIS,
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;;; See the License for the specific language governing permissions and
;;; limitations under the License.
(define-module (chickadee math)
#:export (pi
pi/2
tau
cotan
clamp
min
max
lerp
degrees->radians
radians->degrees)
#:replace (min max))
(define pi (* 4.0 (atan 1.0)))
(define pi/2 (/ pi 2.0))
(define tau (* pi 2.0))
(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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