functions.go

// Copyright 2016 Steven Oud. All rights reserved.
// Use of this source code is governed by a MIT-style license that can be found
// in the LICENSE file.

package mathcat

import (
	"fmt"
	"math"
	"math/rand"
)

type function struct {
	arity int
	fn    func(args []float64) float64
}

type functions map[string]*function

// Functions holds all the function names that are available for use
var Functions []string

var funcs = make(functions)

func (f functions) register(name string, function *function) {
	Functions = append(Functions, name)
	f[name] = function
}

func init() {
	funcs.register("abs", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Abs(args[0])
		},
	})
	funcs.register("ceil", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Ceil(args[0])
		},
	})
	funcs.register("floor", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Floor(args[0])
		},
	})
	funcs.register("sin", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Sin(args[0])
		},
	})
	funcs.register("cos", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Cos(args[0])
		},
	})
	funcs.register("tan", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Tan(args[0])
		},
	})
	funcs.register("asin", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Asin(args[0])
		},
	})
	funcs.register("acos", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Acos(args[0])
		},
	})
	funcs.register("atan", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Atan(args[0])
		},
	})
	funcs.register("log", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Log(args[0])
		},
	})
	funcs.register("max", &function{
		arity: 2,
		fn: func(args []float64) float64 {
			return math.Max(args[0], args[1])
		},
	})
	funcs.register("min", &function{
		arity: 2,
		fn: func(args []float64) float64 {
			return math.Min(args[0], args[1])
		},
	})
	funcs.register("sqrt", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return math.Sqrt(args[0])
		},
	})
	funcs.register("rand", &function{
		arity: 0,
		fn: func(_ []float64) float64 {
			return rand.Float64()
		},
	})
	funcs.register("fact", &function{
		arity: 1,
		fn: func(args []float64) float64 {
			return float64(Factorial(int64(args[0])))
		},
	})
	funcs.register("gcd", &function{
		arity: 2,
		fn: func(args []float64) float64 {
			return Gcd(args[0], args[1])
		},
	})
	funcs.register("list", &function{
		arity: 0,
		fn: func(_ []float64) float64 {
			for _, name := range Functions {
				fmt.Printf(name + " ")
			}
			fmt.Println()
			return 0
		},
	})
}

// Factorial calculates the factorial of number n
func Factorial(n int64) int64 {
	if n <= 1 {
		return 1
	}

	return n * Factorial(n-1)
}

// Gcd calculates the greatest common divisor of the numbers x and y
func Gcd(x, y float64) float64 {
	for y != 0 {
		x, y = y, math.Mod(x, y)
	}

	return x
}