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Diffstat (limited to 'src/pkg/math/atan.go')
| -rw-r--r-- | src/pkg/math/atan.go | 105 |
1 files changed, 0 insertions, 105 deletions
diff --git a/src/pkg/math/atan.go b/src/pkg/math/atan.go deleted file mode 100644 index 7fcc90b8b..000000000 --- a/src/pkg/math/atan.go +++ /dev/null @@ -1,105 +0,0 @@ -// 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 arctangent. -*/ - -// The original C code, the long comment, and the constants below were -// from http://netlib.sandia.gov/cephes/cmath/atan.c, available from -// http://www.netlib.org/cephes/cmath.tgz. -// The go code is a version of the original C. -// -// atan.c -// Inverse circular tangent (arctangent) -// -// SYNOPSIS: -// double x, y, atan(); -// y = atan( x ); -// -// DESCRIPTION: -// Returns radian angle between -pi/2 and +pi/2 whose tangent is x. -// -// Range reduction is from three intervals into the interval from zero to 0.66. -// The approximant uses a rational function of degree 4/5 of the form -// x + x**3 P(x)/Q(x). -// -// ACCURACY: -// Relative error: -// arithmetic domain # trials peak rms -// DEC -10, 10 50000 2.4e-17 8.3e-18 -// IEEE -10, 10 10^6 1.8e-16 5.0e-17 -// -// Cephes Math Library Release 2.8: June, 2000 -// Copyright 1984, 1987, 1989, 1992, 2000 by Stephen L. Moshier -// -// The readme file at http://netlib.sandia.gov/cephes/ says: -// Some software in this archive may be from the book _Methods and -// Programs for Mathematical Functions_ (Prentice-Hall or Simon & Schuster -// International, 1989) or from the Cephes Mathematical Library, a -// commercial product. In either event, it is copyrighted by the author. -// What you see here may be used freely but it comes with no support or -// guarantee. -// -// The two known misprints in the book are repaired here in the -// source listings for the gamma function and the incomplete beta -// integral. -// -// Stephen L. Moshier -// moshier@na-net.ornl.gov - -// xatan evaluates a series valid in the range [0, 0.66]. -func xatan(x float64) float64 { - const ( - P0 = -8.750608600031904122785e-01 - P1 = -1.615753718733365076637e+01 - P2 = -7.500855792314704667340e+01 - P3 = -1.228866684490136173410e+02 - P4 = -6.485021904942025371773e+01 - Q0 = +2.485846490142306297962e+01 - Q1 = +1.650270098316988542046e+02 - Q2 = +4.328810604912902668951e+02 - Q3 = +4.853903996359136964868e+02 - Q4 = +1.945506571482613964425e+02 - ) - z := x * x - z = z * ((((P0*z+P1)*z+P2)*z+P3)*z + P4) / (((((z+Q0)*z+Q1)*z+Q2)*z+Q3)*z + Q4) - z = x*z + x - return z -} - -// satan reduces its argument (known to be positive) -// to the range [0, 0.66] and calls xatan. -func satan(x float64) float64 { - const ( - Morebits = 6.123233995736765886130e-17 // pi/2 = PIO2 + Morebits - Tan3pio8 = 2.41421356237309504880 // tan(3*pi/8) - ) - if x <= 0.66 { - return xatan(x) - } - if x > Tan3pio8 { - return Pi/2 - xatan(1/x) + Morebits - } - return Pi/4 + xatan((x-1)/(x+1)) + 0.5*Morebits -} - -// Atan returns the arctangent, in radians, of x. -// -// Special cases are: -// Atan(±0) = ±0 -// Atan(±Inf) = ±Pi/2 -func Atan(x float64) float64 - -func atan(x float64) float64 { - if x == 0 { - return x - } - if x > 0 { - return satan(x) - } - return -satan(-x) -} |