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Diffstat (limited to 'doc/gawk.texi')
| -rw-r--r-- | doc/gawk.texi | 58 |
1 files changed, 56 insertions, 2 deletions
diff --git a/doc/gawk.texi b/doc/gawk.texi index 6dd00c5f..87e46a5e 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -64,7 +64,7 @@ @c applies to and all the info about who's publishing this edition @c These apply across the board. -@set UPDATE-MONTH January, 2017 +@set UPDATE-MONTH May, 2017 @set VERSION 4.1 @set PATCHLEVEL 4 @@ -908,6 +908,7 @@ particular records in a file and perform operations upon them. * Setting the rounding mode:: How to set the rounding mode. * Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic with @command{gawk}. +* Checking for MPFR:: How to check if MPFR is available. * POSIX Floating Point Problems:: Standards Versus Existing Practice. * Floating point summary:: Summary of floating point discussion. * Extension Intro:: What is an extension. @@ -4988,7 +4989,7 @@ the name by which @command{gawk} was invoked. Here is an example of how this feature may be used: @example -awk ' +gawk ' BEGIN @{ for (i = 0; i < length(PROCINFO["argv"]); i++) print i, PROCINFO["argv"][i] @@ -31226,6 +31227,7 @@ this is the place to be. * FP Math Caution:: Things to know. * Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic with @command{gawk}. +* Checking for MPFR:: How to check if MPFR is available. * POSIX Floating Point Problems:: Standards Versus Existing Practice. * Floating point summary:: Summary of floating point discussion. @end menu @@ -32133,6 +32135,58 @@ word sizes. See @end quotation @end ifset +@node Checking for MPFR +@section How To Check If MPFR Is Available + +@cindex MPFR, checking availability of +@cindex checking for MPFR +Occasionally, you might like to be able to check if @command{gawk} +was invoked with the @option{-M} option, enabling aribtrary-precision +arithmetic. You can do so with the following function, contributed +by Andrew Schorr: + +@example +@c file eg/lib/have_mpfr.awk +# adequate_math_precision --- return true if we have enough bits +@c endfile +@ignore +@c file eg/lib/have_mpfr.awk +# +# Andrew Schorr, aschorr@@telemetry-investments.com, Public Domain +# May 2017 +@c endfile +@end ignore +@c file eg/lib/have_mpfr.awk + +function adequate_math_precision(n) +@{ + return (1 != (1+(1/(2^(n-1))))) +@} +@c endfile +@end example + +Here is code that invokes the function in order to check +if arbitrary-precision arithmetic is available: + +@example +BEGIN @{ + # How many bits of mantissa precision are required + # for this program to function properly? + fpbits = 123 + + # We hope that we were invoked with MPFR enabled. If so, the + # following statement should configure calculations to our desired + # precision. + PREC = fpbits + + if (! adequate_math_precision(fpbits)) @{ + print("Error: insufficient computation precision available.\n" \ + "Try again with the -M argument?") > "/dev/stderr" + exit 1 + @} +@} +@end example + @node POSIX Floating Point Problems @section Standards Versus Existing Practice |