| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package math |
| |
| |
| /* |
| * floating point tangent |
| */ |
| |
| // Tan returns the tangent of x. |
| func Tan(x float64) float64 { |
| // Coefficients are #4285 from Hart & Cheney. (19.74D) |
| const ( |
| P0 = -.1306820264754825668269611177e+5; |
| P1 = .1055970901714953193602353981e+4; |
| P2 = -.1550685653483266376941705728e+2; |
| P3 = .3422554387241003435328470489e-1; |
| P4 = .3386638642677172096076369e-4; |
| Q0 = -.1663895238947119001851464661e+5; |
| Q1 = .4765751362916483698926655581e+4; |
| Q2 = -.1555033164031709966900124574e+3; |
| ) |
| |
| flag := false; |
| sign := false; |
| if x < 0 { |
| x = -x; |
| sign = true; |
| } |
| x = x * (4 / Pi); /* overflow? */ |
| var e float64; |
| e, x = Modf(x); |
| i := int32(e); |
| |
| switch i & 3 { |
| case 1: |
| x = 1 - x; |
| flag = true; |
| |
| case 2: |
| sign = !sign; |
| flag = true; |
| |
| case 3: |
| x = 1 - x; |
| sign = !sign; |
| } |
| |
| xsq := x * x; |
| temp := ((((P4*xsq+P3)*xsq+P2)*xsq+P1)*xsq + P0) * x; |
| temp = temp / (((xsq+Q2)*xsq+Q1)*xsq + Q0); |
| |
| if flag { |
| if temp == 0 { |
| panic(NaN()) |
| } |
| temp = 1 / temp; |
| } |
| if sign { |
| temp = -temp |
| } |
| return temp; |
| } |