NAME

Implements rotate left, rotate right, shift left and shift right operations with carry flag for all C integer types

SYNOPSIS

• "use Bit::ShiftReg qw( bits_of_byte bits_of_short bits_of_int bits_of_long" "LSB_byte MSB_byte LSB_short MSB_short LSB_int MSB_int LSB_long MSB_long" "ROL_byte ROR_byte SHL_byte SHR_byte ROL_short ROR_short SHL_short SHR_short" "ROL_int ROR_int SHL_int SHR_int ROL_long ROR_long SHL_long SHR_long );"

  imports all (or some, by leaving some out) of the available operations and functions

• "use Bit::ShiftReg qw(:all);"

  imports all available operations and functions

• "$version = Bit::ShiftReg::Version();"

  returns the module's version number

• "$bits = bits_of_byte();"

  returns the number of bits in a byte (unsigned char) on your machine

• "$bits = bits_of_short();"

  returns the number of bits in an unsigned short on your machine

• "$bits = bits_of_int();"

  returns the number of bits in an unsigned int on your machine

• "$bits = bits_of_long();"

  returns the number of bits in an unsigned long on your machine

• "$lsb = LSB_byte($value);"

  returns the least significant bit (LSB) of a byte (unsigned char)

• "$msb = MSB_byte($value);"

  returns the most significant bit (MSB) of a byte (unsigned char)

• "$lsb = LSB_short($value);"

  returns the least significant bit (LSB) of an unsigned short

• "$msb = MSB_short($value);"

  returns the most significant bit (MSB) of an unsigned short

• "$lsb = LSB_int($value);"

  returns the least significant bit (LSB) of an unsigned int

• "$msb = MSB_int($value);"

  returns the most significant bit (MSB) of an unsigned int

• "$lsb = LSB_long($value);"

  returns the least significant bit (LSB) of an unsigned long

• "$msb = MSB_long($value);"

  returns the most significant bit (MSB) of an unsigned long

• "$carry = ROL_byte($value);"
• "$carry = ROR_byte($value);"
• "$carry_out = SHL_byte($value,$carry_in);"
• "$carry_out = SHR_byte($value,$carry_in);"
• "$carry = ROL_short($value);"
• "$carry = ROR_short($value);"
• "$carry_out = SHL_short($value,$carry_in);"
• "$carry_out = SHR_short($value,$carry_in);"
• "$carry = ROL_int($value);"
• "$carry = ROR_int($value);"
• "$carry_out = SHL_int($value,$carry_in);"
• "$carry_out = SHR_int($value,$carry_in);"
• "$carry = ROL_long($value);"
• "$carry = ROR_long($value);"
• "$carry_out = SHL_long($value,$carry_in);"
• "$carry_out = SHR_long($value,$carry_in);"

Note that "$value" must be a variable in the calls of the functions ROL, ROR, SHL and SHR, and that the contents of this variable are altered IMPLICITLY by these functions!

Note also that the "carry" input value is always truncated to the least significant bit, i.e., input values for "carry" must be either 0 or 1!

Finally, note that the return values of the functions LSB, MSB, ROL, ROR, SHL and SHR are always either 0 or 1!

DESCRIPTION

The results depend on the number of bits that the integer types unsigned char, unsigned short, unsigned int and unsigned long have on your machine.

The module automatically determines the number of bits of each integer type and adjusts its internal constants accordingly.

How the operations work:

ROL

Rotate Left:

 carry:                           value:

 +---+            +---+---+---+---     ---+---+---+---+
 | 1 |  <---+---  | 1 | 0 | 0 | 1  ...  1 | 0 | 1 | 1 |  <---+
 +---+      |     +---+---+---+---     ---+---+---+---+      |
            |                                                |
            +------------------------------------------------+
    

ROR

Rotate Right:

                        value:                          carry:

        +---+---+---+---     ---+---+---+---+           +---+
 +--->  | 1 | 0 | 0 | 1  ...  1 | 0 | 1 | 1 |  ---+---> | 1 |
 |      +---+---+---+---     ---+---+---+---+     |     +---+
 |                                                |
 +------------------------------------------------+
    

SHL

Shift Left:

 carry                        value:                       carry
  out:                                                      in:
 +---+        +---+---+---+---     ---+---+---+---+        +---+
 | 1 |  <---  | 1 | 0 | 0 | 1  ...  1 | 0 | 1 | 1 |  <---  | 1 |
 +---+        +---+---+---+---     ---+---+---+---+        +---+
    

SHR

Shift Right:

 carry                        value:                       carry
  in:                                                       out:
 +---+        +---+---+---+---     ---+---+---+---+        +---+
 | 1 |  --->  | 1 | 0 | 0 | 1  ...  1 | 0 | 1 | 1 |  --->  | 1 |
 +---+        +---+---+---+---     ---+---+---+---+        +---+
    

EXAMPLE

The only C integer type whose length in bits you can be pretty sure about is probably a byte, since the C standard only prescribes minimum lengths for char, short, int and long and that "sizeof(char)" "<=" "sizeof(short)" "<=" "sizeof(int)" "<=" "sizeof(long)".

How to implement a 4-byte shift register and the 4 operations ROL, ROR, SHL and SHR on it:

First, you need to define 4 byte registers:

  $byte0 = 0;
  $byte1 = 0;
  $byte2 = 0;
  $byte3 = 0;

Then proceed as follows:

ROL

Rotate left:

  $carry = SHL_byte($byte3, SHL_byte($byte2, SHL_byte($byte1,
           SHL_byte($byte0, MSB_byte($byte3)))));
    

ROR

Rotate right:

  $carry = SHR_byte($byte0, SHR_byte($byte1, SHR_byte($byte2,
           SHR_byte($byte3, LSB_byte($byte0)))));
    

SHL

Shift left:

  $carry_out = SHL_byte($byte3, SHL_byte($byte2, SHL_byte($byte1,
               SHL_byte($byte0, $carry_in))));
    

SHR

Shift right:

  $carry_out = SHR_byte($byte0, SHR_byte($byte1, SHR_byte($byte2,
               SHR_byte($byte3, $carry_in))));
    

SEE ALSO

VERSION

AUTHOR

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