Give uses of special bit pertterns in binary coded decimal
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In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of bits, usually four or eight. Special bit patterns are sometimes used for a sign or for other indications (e.g., error or overflow).
If error in representation and computation is the primary concern, rather than
efficiency of conversion to and from display form, a scaled binary representation
may be used, which stores a decimal number as a binary-encoded integer and a
binary-encoded signed decimal exponent. For example, 0.2 can be represented as 2
× 10-1
. This representation allows rapid multiplication and division, but may
require multiplication by a power of 10 during addition and subtraction to align the
decimals. It is particularly appropriate for applications with a fixed number of
decimal places, which do not require adjustment during addition and subtraction
and need not store the exponent explicitly.
Chen-Ho encoding provides a boolean transformation for converting groups of
three BCD-encoded digits to and from 10-bit values that can be efficiently encoded
in hardware with only 2 or 3 gate delays. Densely Packed Decimal is a similar
scheme that deals more efficiently and conveniently with the case where the
number of digits is not a multiple of 3.
If error in representation and computation is the primary concern, rather than
efficiency of conversion to and from display form, a scaled binary representation
may be used, which stores a decimal number as a binary-encoded integer and a
binary-encoded signed decimal exponent. For example, 0.2 can be represented as 2
× 10-1
. This representation allows rapid multiplication and division, but may
require multiplication by a power of 10 during addition and subtraction to align the
decimals. It is particularly appropriate for applications with a fixed number of
decimal places, which do not require adjustment during addition and subtraction
and need not store the exponent explicitly.
Chen-Ho encoding provides a boolean transformation for converting groups of
three BCD-encoded digits to and from 10-bit values that can be efficiently encoded
in hardware with only 2 or 3 gate delays. Densely Packed Decimal is a similar
scheme that deals more efficiently and conveniently with the case where the
number of digits is not a multiple of 3.
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