Matt S Trout > Rakudo-Star-2012.08_001 > math.ops

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NAME ^

math.ops - Mathematical Opcodes

DESCRIPTION ^

Parrot's library of mathematical ops.

To use this library of ops, add this directive to your PIR:

 .loadlib 'math_ops'

General Math

cmod(out INT, in INT, in INT)
cmod(invar PMC, invar PMC, in INT)
cmod(invar PMC, invar PMC, invar PMC)

NOTE: This "uncorrected mod" algorithm uses the C language's built-in mod operator (x % y), which is

    ... the remainder when x is divided by y, and thus is zero
    when y divides x exactly.
    ...
    The direction of truncation for / and the sign of the result
    for % are machine-dependent for negative operands, as is the
    action taken on overflow or underflow.
                                                     -- [1], page 41

Also:

    ... if the second operand is 0, the result is undefined.
    Otherwise, it is always true that (a/b)*b + a%b is equal to z. If
    both operands are non-negative, then the remainder is non-
    negative and smaller than the divisor; if not, it is guaranteed
    only that the absolute value of the remainder is smaller than
    the absolute value of the divisor.
                                                     -- [1], page 205

This op is provided for those who need it (such as speed-sensitive applications with heavy use of mod, but using it only with positive arguments), but a more mathematically useful mod based on ** floor(x/y) and defined with y == 0 is provided by the mod op.

  [1] Brian W. Kernighan and Dennis M. Ritchie, *The C Programming
      Language*, Second Edition. Prentice Hall, 1988.

If the denominator is zero, a 'Divide by zero' exception is thrown.

cmod(out NUM, in NUM, in NUM)
cmod(invar PMC, invar PMC, in NUM)

NOTE: This "uncorrected mod" algorithm uses the built-in C math library's fmod() function, which computes

    ... the remainder of dividing x by y. The return value is
    x - n * y, where n is the quotient of x / y, rounded towards
    zero to an integer.
                                -- fmod() manpage on RedHat Linux 7.0

In addition, fmod() returns

    the remainder, unless y is zero, when the function fails and
    errno is set.

According to page 251 of [1], the result when y is zero is implementation- defined.

This op is provided for those who need it, but a more mathematically useful numeric mod based on floor(x/y) instead of truncate(x/y) and defined with y == 0 is provided by the mod op.

  [1] Brian W. Kernighan and Dennis M. Ritchie, *The C Programming
      Language*, Second Edition. Prentice Hall, 1988.

If the denominator is zero, a 'Divide by zero' exception is thrown.

Pseudorandom number operations

These operations perform various pseudorandom number operations.

rand(out NUM)

Set $1 to a random floating point number between 0 and 1, inclusive.

rand(out INT)

Set $1 to a random integer between [-2^31, 2^31) .

rand(out NUM, in NUM)

Set $1 to a random floating point number between 0 and $2, inclusive.

rand(out INT, in INT)

Set $1 to a integer between 0 and $2, inclusive.

rand(out NUM, in NUM, in NUM)

Set $1 to a random floating point number between $2 and $3, inclusive.

srand(in NUM)

Set the random number seed to $1. $1 is casted to an INTVAL.

srand(in INT)

Set the random number seed to $1.

rand(out INT, in INT, in INT)

Set $1 to a integer between $2 and $3, inclusive.

COPYRIGHT ^

Copyright (C) 2001-2011, Parrot Foundation.

LICENSE ^

This program is free software. It is subject to the same license as the Parrot interpreter itself.

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