Source file src/pkg/math/hypot_port.go
1 // Copyright 2009-2010 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package math 6 7 /* 8 Hypot -- sqrt(p*p + q*q), but overflows only if the result does. 9 See: 10 Cleve Moler and Donald Morrison, 11 Replacing Square Roots by Pythagorean Sums 12 IBM Journal of Research and Development, 13 Vol. 27, Number 6, pp. 577-581, Nov. 1983 14 */ 15 16 // Hypot computes Sqrt(p*p + q*q), taking care to avoid 17 // unnecessary overflow and underflow. 18 // 19 // Special cases are: 20 // Hypot(p, q) = +Inf if p or q is infinite 21 // Hypot(p, q) = NaN if p or q is NaN 22 func hypotGo(p, q float64) float64 { 23 // TODO(rsc): Remove manual inlining of IsNaN, IsInf 24 // when compiler does it for us 25 // special cases 26 switch { 27 case p < -MaxFloat64 || p > MaxFloat64 || q < -MaxFloat64 || q > MaxFloat64: // IsInf(p, 0) || IsInf(q, 0): 28 return Inf(1) 29 case p != p || q != q: // IsNaN(p) || IsNaN(q): 30 return NaN() 31 } 32 if p < 0 { 33 p = -p 34 } 35 if q < 0 { 36 q = -q 37 } 38 39 if p < q { 40 p, q = q, p 41 } 42 43 if p == 0 { 44 return 0 45 } 46 47 pfac := p 48 q = q / p 49 r := q 50 p = 1 51 for { 52 r = r * r 53 s := r + 4 54 if s == 4 { 55 return p * pfac 56 } 57 r = r / s 58 p = p + 2*r*p 59 q = q * r 60 r = q / p 61 } 62 panic("unreachable") 63 }