HackersDelight

java.lang.Object
- cds.healpix.common.math.HackersDelight

```
public final class HackersDelight
extends java.lang.Object
```
Utility class which takes its name from the book "Hacker's Delight" by Henry S. Warren. Jr. We also uses the "Bit Twiddling Hacks" page by Sean Eron Anderson from Standford.

Author:

F.-X Pineau

Field Summary

Fields
Modifier and Type	Field and Description
`static long`	`BUT_EXPONENT_BIT_MASK` Bit mask to isolate all but the sign bit of a long or double.
`static long`	`BUT_SIGN_BIT_MASK_L` Bit mask to isolate all but the sign bit of a long or double.
`static long`	`EXPONENT_BITS_MASK` Bit mask to isolate the sign bit of a long or double.
`static int`	`SIGN_BIT_MASK_I` Bit mask to isolate the sign bit of an int or a float.
`static long`	`SIGN_BIT_MASK_L` Bit mask to isolate the sign bit of a long or double.

Constructor Summary

Constructors
Constructor and Description

HackersDelight()

Constructors
Constructor and Description
`HackersDelight()`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static double`	`abs(double x)`
`static int`	`abs(int x)`
`static long`	`abs(long x)`
`static int`	`doz(int x, int y)` Doz stands for "difference or zero" (see p. 37 of HD).
`static long`	`doz(long x, long y)` Doz stands for "difference or zero" (see p. 37 of HD).
`static int`	`floorInt(double a)`
`static int`	`floorIntN(double a)`
`static int`	`floorIntP(double a)`
`static long`	`floorLong(double a)`
`static long`	`floorLongN(double a)`
`static long`	`floorLongP(double a)`
`long`	`flp2(long x)`
`static double`	`fromBits(long doubleBits)`
`static double`	`halfOf(double x)`
`static boolean`	`isPowOf2(int x)` Determines if an integer is a power of two, exact solution.
`static boolean`	`isPowOf2Fast(int x)` Determines if an integer is a power of two, including 0.
`static void`	`main(java.lang.String[] args)`
`static int`	`max(int x, int y)` Returns the greater of two values.
`static long`	`max(long x, long y)` Returns the greater of two values.
`static int`	`min(int x, int y)` Returns the smaller of two values.
`static long`	`min(long x, long y)` Returns the smaller of two values.
`static int`	`nlz(int x)` Branch-free version of `Integer.numberOfLeadingZeros(int)` (also taken from the HD).
`static long`	`toBits(double x)`

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - SIGN_BIT_MASK_I
```
public static final int SIGN_BIT_MASK_I
```
    Bit mask to isolate the sign bit of an int or a float.
    
    See Also:
    
    Constant Field Values
  - SIGN_BIT_MASK_L
```
public static final long SIGN_BIT_MASK_L
```
    Bit mask to isolate the sign bit of a long or double.
    
    See Also:
    
    Constant Field Values
  - BUT_SIGN_BIT_MASK_L
```
public static final long BUT_SIGN_BIT_MASK_L
```
    Bit mask to isolate all but the sign bit of a long or double.
    
    See Also:
    
    Constant Field Values
  - EXPONENT_BITS_MASK
```
public static final long EXPONENT_BITS_MASK
```
    Bit mask to isolate the sign bit of a long or double.
    
    See Also:
    
    Constant Field Values
  - BUT_EXPONENT_BIT_MASK
```
public static final long BUT_EXPONENT_BIT_MASK
```
    Bit mask to isolate all but the sign bit of a long or double.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - HackersDelight
```
public HackersDelight()
```
- Method Detail
  - isPowOf2
```
public static boolean isPowOf2(int x)
```
    Determines if an integer is a power of two, exact solution. From the "Bit Twiddling Hacks" web page of Sean Eron Anderson, slightly modified.
    
    Parameters:
    
    x - the argument
    
    Returns:
    
    true if the argument is a power of 2 and is different from 0.
  - isPowOf2Fast
```
public static boolean isPowOf2Fast(int x)
```
    Determines if an integer is a power of two, including 0. From the "Bit Twiddling Hacks" web page of Sean Eron Anderson, slightly modified.
    
    Parameters:
    
    x - the argument
    
    Returns:
    
    if the argument is a power of 2 OR if it is 0 (which is not a power of 2). For an exact solution (excluding 0), isPowOf2(int).
  - flp2
```
public long flp2(long x)
```
  - halfOf
```
public static double halfOf(double x)
```
  - toBits
```
public static long toBits(double x)
```
  - fromBits
```
public static double fromBits(long doubleBits)
```
  - abs
```
public static int abs(int x)
```
  - abs
```
public static long abs(long x)
```
  - abs
```
public static double abs(double x)
```
  - floorIntP
```
public static int floorIntP(double a)
```
  - floorIntN
```
public static int floorIntN(double a)
```
  - floorInt
```
public static int floorInt(double a)
```
  - floorLongP
```
public static long floorLongP(double a)
```
  - floorLongN
```
public static long floorLongN(double a)
```
  - floorLong
```
public static long floorLong(double a)
```
  - doz
```
public static int doz(int x,
                      int y)
```
    Doz stands for "difference or zero" (see p. 37 of HD). It returns 0 if x > y, else returns x - y, so it can be replace by (x - y) > 0 ? x - y : 0
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    0 if x > y, else returns x - y.
  - doz
```
public static long doz(long x,
                       long y)
```
    Doz stands for "difference or zero" (see p. 37 of HD). It returns 0 if x > y, else returns x - y, so it can be replace by (x - y) > 0 ? x - y : 0
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    0 if x > y, else returns x - y.
  - min
```
public static int min(int x,
                      int y)
```
    Returns the smaller of two values.
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    the smaller of two values.
  - min
```
public static long min(long x,
                       long y)
```
    Returns the smaller of two values.
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    the smaller of two values.
  - max
```
public static int max(int x,
                      int y)
```
    Returns the greater of two values.
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    the greater of two values.
  - max
```
public static long max(long x,
                       long y)
```
    Returns the greater of two values.
    
    Parameters:
    
    x - an argument
    
    y - another argument
    
    Returns:
    
    the greater of two values.
  - nlz
```
public static int nlz(int x)
```
    Branch-free version of Integer.numberOfLeadingZeros(int) (also taken from the HD). See "Number of leading zeros, branch-free binary search" in HD.
    
    Parameters:
    
    x - the argument
    
    Returns:
    
    the number of leading zeros in the given argument.
  - main
```
public static void main(java.lang.String[] args)
```

Class HackersDelight

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

SIGN_BIT_MASK_I

SIGN_BIT_MASK_L

BUT_SIGN_BIT_MASK_L

EXPONENT_BITS_MASK

BUT_EXPONENT_BIT_MASK

Constructor Detail

HackersDelight

Method Detail

isPowOf2

isPowOf2Fast

flp2

halfOf

toBits

fromBits

abs

abs

abs

floorIntP

floorIntN

floorInt

floorLongP

floorLongN

floorLong

doz

doz

min

min

max

max

nlz

main