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Diffstat (limited to 'doc/manual.txt')
| -rwxr-xr-x | doc/manual.txt | 63 |
1 files changed, 52 insertions, 11 deletions
diff --git a/doc/manual.txt b/doc/manual.txt index 8399dc4b0..391f319a1 100755 --- a/doc/manual.txt +++ b/doc/manual.txt @@ -47,7 +47,7 @@ components called `locations`:idx:. A variable is basically a name for a location. Each variable and location is of a certain `type`:idx:. The variable's type is called `static type`:idx:, the location's type is called `dynamic type`:idx:. If the static type is not the same as the dynamic type, -it is a supertype or subtype of the dynamic type. +it is a super-type or subtype of the dynamic type. An `identifier`:idx: is a symbol declared as a name for a variable, type, procedure, etc. The region of the program over which a declaration applies is @@ -424,8 +424,8 @@ Integers, bool, characters and enumeration types (and subrange of these types) belong to ordinal types. -Pre-defined numerical types -~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Pre-defined integer types +~~~~~~~~~~~~~~~~~~~~~~~~~ These integer types are pre-defined: ``int`` @@ -469,6 +469,14 @@ operation meaning ``int32`` type) ====================== ====================================================== +`Automatic type conversion`:idx: is performed in expressions where different +kinds of integer types are used: the smaller type is converted to the larger. +For further details, see `Convertible relation`_. + + +Pre-defined floating point types +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + The following floating point types are pre-defined: ``float`` @@ -482,16 +490,49 @@ floatXX implementation supports ``float32`` and ``float64``. Literals of these types have the suffix 'fXX. -`Automatic type conversion`:idx: is performed in expressions where different -kinds of integer types are used. However, if the type conversion -loses information, the `EOutOfRange`:idx: exception is raised (if the error -cannot be detected at compile time). Automatic type conversion in expressions with different kinds -of floating point types is performed: the smaller type is -converted to the larger. Arithmetic performed on floating point types -follows the IEEE standard. Integer types are not converted to floating point -types automatically and vice versa. +of floating point types is performed: See `Convertible relation`_ for further +details. Arithmetic performed on floating point types follows the IEEE +standard. Integer types are not converted to floating point types automatically +and vice versa. + +The IEEE standard defines five types of floating-point exceptions: + +* Invalid: operations with mathematically invalid operands, + for example 0.0/0.0, sqrt(-1.0), and log(-37.8). +* Division by zero: divisor is zero and dividend is a finite nonzero number, + for example 1.0/0.0. +* Overflow: operation produces a result that exceeds the range of the exponent, + for example MAXDOUBLE+0.0000000000001e308. +* Underflow: operation produces a result that is too small to be represented + as a normal number, for example, MINDOUBLE * MINDOUBLE. +* Inexact: operation produces a result that cannot be represented with infinite + precision, for example, 2.0 / 3.0, log(1.1) and 0.1 in input. + +The IEEE exceptions are either ignored at runtime or mapped to the +Nimrod exceptions: `EFloatInvalidOp`:idx, `EFloatDivByZero`:idx:, +`EFloatOverflow`:idx:, `EFloatUnderflow`:idx:, and `EFloatInexact`:idx:\. +These exceptions inherit from the `EFloatingPoint`:idx: base class. + +Nimrod provides the pragmas `NaNChecks`:idx and `InfChecks`:idx:\ to control +whether the IEEE exceptions are ignored or trap a Nimrod exception: + +.. code-block:: nimrod + {.NanChecks: on, InfChecks: on.} + var a = 1.0 + var b = 0.0 + echo b / b # raises EFloatInvalidOp + echo a / b # raises EFloatOverflow + +In the current implementation ``EFloatDivByZero`` and ``EFloatInexact`` are +never raised. ``EFloatOverflow`` is raised instead of ``EFloatDivByZero``. +There is also a `floatChecks`:idx: pragma that is a short-cut for the +combination of ``NaNChecks`` and ``InfChecks`` pragmas. ``floatChecks`` are +turned off as default. + +The only operations that are affected by the ``floatChecks`` pragma are +the ``+``, ``-``, ``*``, ``/`` operators for floating point types. Boolean type |