Arithmetic functions are terms which are evaluated by the arithmetic
predicates described above. SWI-Prolog tries to hide the difference
between integer arithmetic and floating point arithmetic from the Prolog
user. Arithmetic is done as integer arithmetic as long as possible and
converted to floating point arithmetic whenever one of the arguments or
the combination of them requires it. If a function returns a floating
point value which is whole it is automatically transformed into an
integer. There are three types of arguments to functions:
| Expr | Arbitrary expression,
returning either a floating point value or an integer. |
| IntExpr | Arbitrary expression that
should evaluate into an integer. |
| Int | An integer. |
In case integer addition, subtraction and multiplication would lead
to an integer overflow the operands are automatically converted to
floating point numbers. The floating point functions (sin/1, exp/1,
etc.) form a direct interface to the corresponding C library functions
used to compile SWI-Prolog. Please refer to the C library documentation
for details on precision, error handling, etc.
- - +Expr
-
Result = -Expr
- +Expr1 + +Expr2
-
Result = Expr1 + Expr2
- +Expr1 - +Expr2
-
Result = Expr1 - Expr2
- +Expr1 * +Expr2
-
Result = Expr1 × Expr2
- +Expr1 / +Expr2
-
Result = Expr1/Expr2
- +IntExpr1 mod +IntExpr2
-
Modulo:
Result = IntExpr1 - (IntExpr1 // IntExpr2) × IntExpr2
The function mod/2
is implemented using the C
% operator. It's behaviour with
negtive values is illustrated in the table below.
| 2 | = | 17 | mod | 5 |
| 2 | = | 17 | mod | -5 |
| -2 | = | -17 | mod | 5 |
| -2 | = | -17 | mod | 5 |
- +IntExpr1 rem +IntExpr2
-
Remainder of division:
Result = float_fractional_part(IntExpr1/IntExpr2)
- +IntExpr1 // +IntExpr2
-
Integer division:
Result = truncate(Expr1/Expr2)
- abs(+Expr)
-
Evaluate Expr and return the absolute value of it.
- sign(+Expr)
-
Evaluate to -1 if Expr < 0, 1 if Expr
> 0 and 0 if
Expr = 0.
- max(+Expr1, +Expr2)
-
Evaluates to the largest of both Expr1 and Expr2.
- min(+Expr1, +Expr2)
-
Evaluates to the smallest of both Expr1 and Expr2.
- .(+Int,)
-
A list of one element evaluates to the element. This implies
"a"
evaluates to the ASCII value of the letter `a' (97). This option is
available for compatibility only. It will not work if `style_check(+string)'
is active as "a" will then be transformed into a string
object. The recommended way to specify the ASCII value of the letter `a'
is 0'a.
- random(+Int)
-
Evaluates to a random integer i for which 0 =< i < Int.
The seed of this random generator is determined by the system clock when
SWI-Prolog was started.
- round(+Expr)
-
Evaluates Expr and rounds the result to the nearest integer.
- integer(+Expr)
-
Same as round/1
(backward compatibility).
- float(+Expr)
-
Translate the result to a floating point number. Normally, Prolog will
use integers whenever possible. When used around the 2nd argument of
is/2, the
result will be returned as a floating point number. In other contexts,
the operation has no effect.
- float_fractional_part(+Expr)
-
Fractional part of a floating-point number. Negative if Expr
is negative, 0 if Expr is integer.
- float_integer_part(+Expr)
-
Integer part of floating-point number. Negative if Expr is
negative, Expr if Expr is integer.
- truncate(+Expr)
-
Truncate Expr to an integer. Same as float_integer_part/1.
- floor(+Expr)
-
Evaluates Expr and returns the largest integer smaller or
equal to the result of the evaluation.
- ceiling(+Expr)
-
Evaluates Expr and returns the smallest integer larger or
equal to the result of the evaluation.
- ceil(+Expr)
-
Same as ceiling/1
(backward compatibility).
- +IntExpr >> +IntExpr
-
Bitwise shift IntExpr1 by IntExpr2 bits to the
right.
- +IntExpr << +IntExpr
-
Bitwise shift IntExpr1 by IntExpr2 bits to the
left.
- +IntExpr \/ +IntExpr
-
Bitwise `or' IntExpr1 and IntExpr2.
- +IntExpr /\ +IntExpr
-
Bitwise `and' IntExpr1 and IntExpr2.
- +IntExpr xor +IntExpr
-
Bitwise `exclusive or' IntExpr1 and IntExpr2.
- \ +IntExpr
-
Bitwise negation.
- sqrt(+Expr)
-
Result = sqrt(Expr)
- sin(+Expr)
-
Result = sin(Expr). Expr is
the angle in radians.
- cos(+Expr)
-
Result = cos(Expr). Expr is
the angle in radians.
- tan(+Expr)
-
Result = tan(Expr). Expr is
the angle in radians.
- asin(+Expr)
-
Result = arcsin(Expr). Result
is the angle in radians.
- acos(+Expr)
-
Result = arccos(Expr). Result
is the angle in radians.
- atan(+Expr)
-
Result = arctan(Expr). Result
is the angle in radians.
- atan(+YExpr, +XExpr)
-
Result = arctan(YExpr/XExpr). Result
is the angle in radians. The return value is in the range [- pi ...
pi ]. Used to convert between rectangular and polar coordinate
system.
- log(+Expr)
-
Result = ln(Expr)
- log10(+Expr)
-
Result = log10(Expr)
- exp(+Expr)
-
Result = e **Expr
- +Expr1 ** +Expr2
-
Result = Expr1**Expr2
- +Expr1 ^ +Expr2
-
Same as **/2. (backward compatibility).
- pi
-
Evaluates to the mathematical constant pi (3.141593).
- e
-
Evaluates to the mathematical constant e (2.718282).
- cputime
-
Evaluates to a floating point number expressing the CPU
time (in seconds) used by Prolog up till now. See also statistics/2
and time/1.