src/usr.bin/awk/awk.1 - diff

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Diff for /src/usr.bin/awk/awk.1 between version 1.58 and 1.59

-version 1.58, 2020/11/05 16:04:39
+version 1.59, 2020/12/09 20:00:11
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 Line 280
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  .Pq indicated by whitespace .
  The operators
  .Ic \&! ++ \-\- += \-= *= /= %= ^=
- .Ic > >= < <= == != ?:
+ .Ic > >= < <= == != ?\&:
  are also available in expressions.
  Variables may be scalars, array elements
  (denoted
 Line 919
 Line 919
 Line 919
  .Bd -literal -offset indent
  { print "error!" > "/dev/stderr" }
  .Ed
+ .Sh UNUSUAL FLOATING-POINT VALUES
+ .Nm
+ was designed before IEEE 754 arithmetic defined Not-A-Number (NaN)
+ and Infinity values, which are supported by all modern floating-point
+ hardware.
+ .Pp
+ Because
+ .Nm
+ uses
+ .Xr strtod 3
+ and
+ .Xr atof 3
+ to convert string values to double-precision floating-point values,
+ modern C libraries also convert strings starting with
+ .Dv inf
+ and
+ .Dv nan
+ into infinity and NaN values respectively.
+ This led to strange results,
+ with something like this:
+ .Pp
+ .Li echo nancy | awk '{ print $1 + 0 }'
+ .Pp
+ printing
+ .Dv nan
+ instead of zero.
+ .Pp
+ .Nm
+ now follows GNU
+ .Nm ,
+ and prefilters string values before attempting
+ to convert them to numbers, as follows:
+ .Bl -tag -width Ds
+ .It Hexadecimal values
+ Hexadecimal values (allowed since C99) convert to zero, as they did
+ prior to C99.
+ .It NaN values
+ The two strings
+ .Dq +NAN
+ and
+ .Dq -NAN
+ (case independent) convert to NaN.
+ No others do.
+ (NaNs can have signs.)
+ .It Infinity values
+ The two strings
+ .Dq +INF
+ and
+ .Dq -INF
+ (case independent) convert to positive and negative infinity, respectively.
+ No others do.
+ .El
  .Sh SEE ALSO
  .Xr cut 1 ,
  .Xr date 1 ,