# Ada '83 Language Reference Manual

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## 4.10. Universal Expressions

A universal_expression is either an expression that delivers a result of
type universal_integer or one that delivers a result of type
universal_real.

The same operations are predefined for the type universal_integer as for
any integer type. The same operations are predefined for the type
universal_real as for any floating point type. In addition, these
operations include the following multiplication and division operators:

Operator Operation Left operand Right operand Result type
type type
* multiply universal_real universal_integer universal_real
universal_integer universal_real universal_real
/ divide universal_real universal_integer universal_real

The accuracy of the evaluation of a universal expression of type
universal_real is at least as good as that of the most accurate predefined
floating point type supported by the implementation, apart from
universal_real itself. Furthermore, if a universal expression is a static
expression, then the evaluation must be exact.

For the evaluation of an operation of a nonstatic universal expression, an
implementation is allowed to raise the exception NUMERIC_ERROR only if the
result of the operation is a real value whose absolute value exceeds the
largest safe number of the most accurate predefined floating point type
(excluding universal_real), or an integer value greater than SYSTEM.MAX_INT
or less than SYSTEM.MIN_INT.

Note:

It is a consequence of the above rules that the type of a universal
expression is universal_integer if every primary contained in the
expression is of this type (excluding actual parameters of attributes that
are functions, and excluding right operands of exponentiation operators)
and that otherwise the type is universal_real.

Examples:

1 + 1 -- 2
abs(-10)*3 -- 30
KILO : constant := 1000;
MEGA : constant := KILO*KILO; -- 1_000_000
LONG : constant := FLOAT'DIGITS*2;
HALF_PI : constant := PI/2; -- see 3.2.2
DEG_TO_RAD : constant := HALF_PI/90;
RAD_TO_DEG : constant := 1.0/DEG_TO_RAD; -- equivalent to
1.0/((3.14159_26536/2)/90)

**References:** actual parameter,
attribute,
evaluation of an expression,
floating point type,
function,
integer type,
multiplying operator,
and 4.5.5,
predefined operation,
primary,
real type,
safe number,
system.max_int,
system.min_int,
type,
universal_integer type,
universal_real type.
**Rationale references:**
3.6 Expressions

Address any questions or comments to
adainfo@sw-eng.falls-church.va.us.