issue17005.go

     1  // compile
     2  
     3  // Copyright 2016 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // This tickles (a version of) the PPC64 back end to
     8  // emit a BVS instruction.
     9  
    10  package foo
    11  
    12  type Flag int
    13  
    14  const (
    15  	Identity  Flag = iota - 2 // H is the identity matrix; no rotation is needed.
    16  	Rescaling                 // H specifies rescaling.
    17  )
    18  
    19  type DrotmParams struct {
    20  	Flag
    21  }
    22  
    23  func Drotmg(d1, d2, x1, y1 float64) (p DrotmParams, rd1, rd2, rx1 float64) {
    24  
    25  	const (
    26  		gam    = 4.0
    27  		gamsq  = 16.0
    28  		rgamsq = 5e-8
    29  	)
    30  
    31  	if d1 < 0 {
    32  		p.Flag = Rescaling
    33  		return
    34  	}
    35  
    36  	for rd1 <= rgamsq || rd1 >= gamsq {
    37  		if rd1 <= rgamsq {
    38  			rd1 *= gam * gam
    39  			rx1 /= gam
    40  		} else {
    41  			rd1 /= gam * gam
    42  			rx1 *= gam
    43  		}
    44  	}
    45  	return
    46  }
    47
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