Next: Setting the rounding mode, Previous: Try To Round, Up: FP Math Caution [Contents][Index]

`gawk`

uses a global working precision; it does not keep track of
the precision or accuracy of individual numbers. Performing an arithmetic
operation or calling a built-in function rounds the result to the current
working precision. The default working precision is 53 bits, which you can
modify using the predefined variable `PREC`

. You can also set the
value to one of the predefined case-insensitive strings
shown in Table 15.4,
to emulate an IEEE 754 binary format.

`PREC` | IEEE 754 binary format |
---|---|

`"half"` | 16-bit half-precision |

`"single"` | Basic 32-bit single precision |

`"double"` | Basic 64-bit double precision |

`"quad"` | Basic 128-bit quadruple precision |

`"oct"` | 256-bit octuple precision |

The following example illustrates the effects of changing precision on arithmetic operations:

$gawk -M -v PREC=100 'BEGIN { x = 1.0e-400; print x + 0>PREC = "double"; print x + 0 }'-| 1e-400 -| 0

CAUTION:Be wary of floating-point constants! When reading a floating-point constant from program source code,`gawk`

uses the default precision (that of a C`double`

), unless overridden by an assignment to the special variable`PREC`

on the command line, to store it internally as an MPFR number. Changing the precision using`PREC`

in the program text doesnotchange the precision of a constant.If you need to represent a floating-point constant at a higher precision than the default and cannot use a command-line assignment to

`PREC`

, you should either specify the constant as a string, or as a rational number, whenever possible. The following example illustrates the differences among various ways to print a floating-point constant:$gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 0.1) }'-| 0.1000000000000000055511151 $gawk -M -v PREC=113 'BEGIN { printf("%0.25f\n", 0.1) }'-| 0.1000000000000000000000000 $gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", "0.1") }'-| 0.1000000000000000000000000 $gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 1/10) }'-| 0.1000000000000000000000000

Next: Setting the rounding mode, Previous: Try To Round, Up: FP Math Caution [Contents][Index]