4.5.5 Multiplying Operators

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Static Semantics

The multiplying operators * (multiplication), / (division), mod (modulus), and rem (remainder) are predefined for every specific integer type T:

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

Signed integer multiplication has its conventional meaning.

Signed integer division and remainder are defined by the relation:

A = (A/B)*B + (A rem B)

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:

(-A)/B = -(A/B) = A/(-B)

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:

A = B*N + (A mod B)

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).

Multiplication and division operators are predefined for every specific floating point type T:

function "*"(Left, Right T) return T
function "/"(Left, Right T) return T

The following multiplication and division operators, with an operand of the predefined type Integer, are predefined for every specific fixed point type T:

function "*"(Left T; Right Integer) return T
function "*"(Left Integer; Right T) return T
function "/"(Left T; Right Integer) return T

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:

function "*"(Left, Right root_real) return root_real
function "/"(Left, Right root_real) return root_real

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

Multiplication and division between any two fixed point types are provided by the following two predefined operators:

function "*"(Left, Right universal_fixed) return universal_fixed
function "/"(Left, Right universal_fixed) return universal_fixed

Legality Rules

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

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.

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 TMachine_Overflows True, division by zero raises Constraint_Error.


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:

A  rem (-B) =   A rem B 
(-A) rem   B  = -(A rem B)

18  For any signed integer K, the following identity holds:

A mod B   =   (A + K*B) mod B

The relations between signed integer division, remainder, and modulus are illustrated by the following table:

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        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

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 of expressions involving multiplying operators:

I : Integer := 1; 
J : Integer := 2; 
K : Integer := 3;

X : Real := 1.0;                      --     see 3.5.7 
Y : Real := 2.0;

F : Fraction := 0.25;                 --     see 3.5.9 
G : Fraction := 0.5;

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

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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual