Multiplying Operators
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

Contents Index Search Previous Next

# 4.5.5 Multiplying Operators

#### Static Semantics

1
The multiplying operators * (multiplication), / (division), mod (modulus), and rem (remainder) are predefined for every specific integer type T:
2
`function "*" (Left, Right : T) return T
function "/" (Left, Right : T) return T
function "mod"(Left, Right : T) return T
function "rem"(Left, Right : T) return T`
3
Signed integer multiplication has its conventional meaning.
4
Signed integer division and remainder are defined by the relation:
5
`A = (A/B)*B + (A rem B)`
6
where (A rem B) has the sign of A and an absolute value less than the absolute value of B. Signed integer division satisfies the identity:
7
`(-A)/B = -(A/B) = A/(-B)`
8
The signed integer modulus operator is defined such that the result of A mod B has the sign of B and an absolute value less than the absolute value of B; in addition, for some signed integer value N, this result satisfies the relation:
9
`A = B*N + (A mod B)`
10
The multiplying operators on modular types are defined in terms of the corresponding signed integer operators, followed by a reduction modulo the modulus if the result is outside the base range of the type (which is only possible for the "*" operator).
11
Multiplication and division operators are predefined for every specific floating point type T:
12
`function "*"(Left, Right : T) return T
function "/"(Left, Right : T) return T`
13
The following multiplication and division operators, with an operand of the predefined type Integer, are predefined for every specific fixed point type T:
14
`function "*"(Left : T; Right : Integer) return T
function "*"(Left : Integer; Right : T) return T
function "/"(Left : T; Right : Integer) return T`
15
All of the above multiplying operators are usable with an operand of an appropriate universal numeric type. The following additional multiplying operators for root_real are predefined, and are usable when both operands are of an appropriate universal or root numeric type, and the result is allowed to be of type root_real, as in a number_declaration:
16
`function "*"(Left, Right : root_real) return root_real
function "/"(Left, Right : root_real) return root_real`
17
`function "*"(Left : root_real; Right : root_integer) return root_real
function "*"(Left : root_integer; Right : root_real) return root_real
function "/"(Left : root_real; Right : root_integer) return root_real`
18
Multiplication and division between any two fixed point types are provided by the following two predefined operators:
19
`function "*"(Left, Right : universal_fixed) return universal_fixed
function "/"(Left, Right : universal_fixed) return universal_fixed`

#### Legality Rules

20
The above two fixed-fixed multiplying operators shall not be used in a context where the expected type for the result is itself universal_fixed -- the context has to identify some other numeric type to which the result is to be converted, either explicitly or implicitly.

#### Dynamic Semantics

21
The multiplication and division operators for real types have their conventional meaning. For floating point types, the accuracy of the result is determined by the precision of the result type. For decimal fixed point types, the result is truncated toward zero if the mathematical result is between two multiples of the small of the specific result type (possibly determined by context); for ordinary fixed point types, if the mathematical result is between two multiples of the small, it is unspecified which of the two is the result.
22
The exception Constraint_Error is raised by integer division, rem, and mod if the right operand is zero. Similarly, for a real type T with T'Machine_Overflows True, division by zero raises Constraint_Error.
NOTES
23
17 For positive A and B, A/B is the quotient and A rem B is the remainder when A is divided by B. The following relations are satisfied by the rem operator:
24
`A rem (-B) = A rem B
(-A) rem B = -(A rem B)`
25
18 For any signed integer K, the following identity holds:
26
`A mod B = (A + K*B) mod B`
27
The relations between signed integer division, remainder, and modulus are illustrated by the following table:
28
`A B A/B A rem B A mod B A B A/B A rem B A mod B`
29
`10 5 2 0 0 -10 5 -2 0 0
11 5 2 1 1 -11 5 -2 -1 4
12 5 2 2 2 -12 5 -2 -2 3
13 5 2 3 3 -13 5 -2 -3 2
14 5 2 4 4 -14 5 -2 -4 1`
30
`A B A/B A rem B A mod B A B A/B A rem B A mod B
10 -5 -2 0 0 -10 -5 2 0 0
11 -5 -2 1 -4 -11 -5 2 -1 -1
12 -5 -2 2 -3 -12 -5 2 -2 -2
13 -5 -2 3 -2 -13 -5 2 -3 -3
14 -5 -2 4 -1 -14 -5 2 -4 -4`

#### Examples

31
Examples of expressions involving multiplying operators:
32
`I : Integer := 1;
J : Integer := 2;
K : Integer := 3;`
33
`X : Real := 1.0; -- see 3.5.7
Y : Real := 2.0;`
34
`F : Fraction := 0.25; -- see 3.5.9
G : Fraction := 0.5;`
35
`Expression Value Result Type
I*J 2 same as I and J, that is, Integer
K/J 1 same as K and J, that is, Integer
K mod J 1 same as K and J, that is, Integer
X/Y 0.5 same as X and Y, that is, Real
F/2 0.125 same as F, that is, Fraction
3*F 0.75 same as F, that is, Fraction
0.75*G 0.375 universal_fixed, implicitly convertible
to any fixed point type
Fraction(F*G) 0.125 Fraction, as stated by the conversion
Real(J)*Y 4.0 Real, the type of both operands after
conversion of J`

Contents Index Search Previous Next Legal