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authorRaymond Hettinger <python@rcn.com>2005-07-01 16:54:12 (GMT)
committerRaymond Hettinger <python@rcn.com>2005-07-01 16:54:12 (GMT)
commit87de8ed4b929d338fca743347df5b7100ead1ae0 (patch)
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parent62cc1233f9796222cce9638333546357920c6d3d (diff)
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More info on rounding modes. Add sections for floating point notes.
Diffstat (limited to 'Doc/lib')
-rw-r--r--Doc/lib/libdecimal.tex19
1 files changed, 12 insertions, 7 deletions
diff --git a/Doc/lib/libdecimal.tex b/Doc/lib/libdecimal.tex
index 6e46c11..bcd5b2b 100644
--- a/Doc/lib/libdecimal.tex
+++ b/Doc/lib/libdecimal.tex
@@ -501,13 +501,15 @@ with the \class{Context} constructor.
arithmetic operations in the context.
The \var{rounding} option is one of:
- \constant{ROUND_CEILING} (towards \constant{Infinity}),
- \constant{ROUND_DOWN} (towards zero),
- \constant{ROUND_FLOOR} (towards \constant{-Infinity}),
- \constant{ROUND_HALF_DOWN} (towards zero),
- \constant{ROUND_HALF_EVEN},
- \constant{ROUND_HALF_UP} (away from zero), or
- \constant{ROUND_UP} (away from zero).
+ \begin{itemize}
+ \item \constant{ROUND_CEILING} (towards \constant{Infinity}),
+ \item \constant{ROUND_DOWN} (towards zero),
+ \item \constant{ROUND_FLOOR} (towards \constant{-Infinity}),
+ \item \constant{ROUND_HALF_DOWN} (to nearest with ties going towards zero),
+ \item \constant{ROUND_HALF_EVEN} (to nearest with ties going to nearest even integer),
+ \item \constant{ROUND_HALF_UP} (to nearest with ties going away from zero), or
+ \item \constant{ROUND_UP} (away from zero).
+ \end{itemize}
The \var{traps} and \var{flags} fields list any signals to be set.
Generally, new contexts should only set traps and leave the flags clear.
@@ -834,6 +836,8 @@ The following table summarizes the hierarchy of signals:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Floating Point Notes \label{decimal-notes}}
+\subsubsection{Mitigating round-off error with increased precision}
+
The use of decimal floating point eliminates decimal representation error
(making it possible to represent \constant{0.1} exactly); however, some
operations can still incur round-off error when non-zero digits exceed the
@@ -881,6 +885,7 @@ Decimal("0.0060000")
Decimal("0.0060000")
\end{verbatim}
+\subsubsection{Special values}
The number system for the \module{decimal} module provides special
values including \constant{NaN}, \constant{sNaN}, \constant{-Infinity},