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package main
import (
"fmt"
"math"
)
// parseFunction returns nil is fn is not a valid function.
func parseFunction(fn string) func(*Calculator) {
switch fn {
case "sin", "cos", "tan":
return trig(fn)
case "asin", "acos", "atan":
return invTrig(fn)
case "deg":
return apply(radToDeg)
case "rad":
return apply(degToRad)
case "fac":
return apply(func(x float64) float64 {
if !isUint(x) {
return x
}
return float64(factorial(uint(x)))
})
case "ch": // choose
return combination
case "log10":
return apply(math.Log10)
case "log2":
return apply(math.Log2)
case "ln":
return apply(math.Log)
}
return nil
}
// apply returns a function that applies fn to the bottom stack element of the
// calculator.
func apply(fn func(float64) float64) func(*Calculator) {
return func(c *Calculator) {
x, err := c.stack.pop()
if err != nil {
return
}
c.stack.push(fn(x))
}
}
// trig returns a closure that performs the trig function specified by fn.
// Panics if fn is not one of "sin", "cos" or "tan".
func trig(fn string) func(*Calculator) {
return func(c *Calculator) {
if len(c.stack) <= 0 {
return
}
v := &c.stack[len(c.stack)-1]
// The math package expects arguments to trig functions to be in radians.
if c.angleMode == degrees {
*v = degToRad(*v)
}
switch fn {
case "sin":
*v = math.Sin(*v)
case "cos":
*v = math.Cos(*v)
case "tan":
*v = math.Tan(*v)
default:
panic(fmt.Sprintf("invalid trig function: '%s'", fn))
}
}
}
// invTrig returns a closure that performs the inverse trig function specified
// by fn. Panics if fn is not one of "asin", "acos" or "atan".
func invTrig(fn string) func(*Calculator) {
return func(c *Calculator) {
if len(c.stack) <= 0 {
return
}
v := &c.stack[len(c.stack)-1]
switch fn {
case "asin":
*v = math.Asin(*v)
case "acos":
*v = math.Acos(*v)
case "atan":
*v = math.Atan(*v)
default:
panic(fmt.Sprintf("invalid inverse trig function: '%s'", fn))
}
if c.angleMode == degrees {
*v = radToDeg(*v)
}
}
}
func degToRad(deg float64) (rad float64) {
return deg * math.Pi / 180.0
}
func radToDeg(rad float64) (deg float64) {
return rad * 180 / math.Pi
}
// factorial returns n! (n factorial).
func factorial(n uint) uint {
if n == 0 {
return 1
}
// n! = n*(n-1)!
for i := n - 1; i > 1; i-- {
n *= i
}
return n
}
// Combination function. "n choose k" with integers n and k such that n >= k >= 0.
func combination(c *Calculator) {
k, err := c.stack.pop()
if err != nil {
return
}
if !isUint(k) { // undefined on non-ints
c.stack.push(k)
return
}
n, err := c.stack.pop()
if err != nil {
c.stack.push(k)
return
}
if !isUint(n) { // undefined on non-ints
c.stack.push(n)
return
}
if k > n || n < 0 || k < 0 {
c.stack.push(n)
c.stack.push(k)
} else {
n, k := uint(n), uint(k)
c.stack.push(float64(factorial(n) / (factorial(k) * factorial(n-k))))
}
}
func isUint(n float64) bool {
return float64(uint(n)) == n
}
|