diff options
Diffstat (limited to 'Doc/lib')
| -rw-r--r-- | Doc/lib/libdecimal.tex | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/Doc/lib/libdecimal.tex b/Doc/lib/libdecimal.tex index d573f44..562aae6 100644 --- a/Doc/lib/libdecimal.tex +++ b/Doc/lib/libdecimal.tex @@ -22,7 +22,7 @@ arithmetic. It offers several advantages over the \class{float()} datatype: \item Decimal numbers can be represented exactly. In contrast, numbers like \constant{1.1} do not have an exact representation in binary floating point. -End users typically wound not expect \constant{1.1} to display as +End users typically would not expect \constant{1.1} to display as \constant{1.1000000000000001} as it does with binary floating point. \item The exactness carries over into arithmetic. In decimal floating point, @@ -538,7 +538,19 @@ large number of methods for doing arithmetic directly in a given context. rounding method, flags, and traps are applied to the conversion. This is useful because constants are often given to a greater precision than - is needed by the application. + is needed by the application. Another benefit is that rounding immediately + eliminates unintended effects from digits beyond the current precision. + In the following example, using unrounded inputs means that adding zero + to a sum can change the result: + + \begin{verbatim} + >>> getcontext().prec = 3 + >>> Decimal("3.4445") + Decimal("1.0023") + Decimal("4.45") + >>> Decimal("3.4445") + Decimal(0) + Decimal("1.0023") + Decimal("4.44") + \end{verbatim} + \end{methoddesc} \begin{methoddesc}{Etiny}{} @@ -612,12 +624,14 @@ here. \begin{methoddesc}{normalize}{x} Normalize reduces an operand to its simplest form. - Essentially a plus operation with all trailing zeros removed from the - result. + Essentially a \method{plus} operation with all trailing zeros removed from + the result. \end{methoddesc} \begin{methoddesc}{plus}{x} - Minus corresponds to the unary prefix plus operator in Python. + Plus corresponds to the unary prefix plus operator in Python. This + operation applies the context precision and rounding, so it is + \emph{not} an identity operation. \end{methoddesc} \begin{methoddesc}{power}{x, y\optional{, modulo}} |