Level Epsilon Architecture Support Reference Manual

Data Structure and Text
Second word:
[ext] Not used
hi_order_exp [47: 9] The high order 9 bits of the exponent
mantissa [38:39] The fractional portion of the mantissa
A double precision floating point operand with an exponent equal to 13 is used as a
canonical representation of a double precision integer; an operand in this form is called a
double_integer. (A double precision operand with exponent and mantissa zero is also a
valid double_integer.) The largest double_integer magnitude is 2**78-1 = 8*26-1.
Decimal Sequence Operands
Some operators generate or consume operands interpreted as a sequence of decimal
digits. Each digit is represented as a 4-bit binary integer in the range {0 to 9}. (Hex
sequence representations of decimal data are often called Binary Coded Decimal, BCD.)
A digit sequence is an unsigned sequence of decimal digits. Digit sequences generated
by binary-to-decimal conversion operators contain only true digits; however, digit
sequences that are inputs to pointer operators may include nondigits, which are hex
characters in the range {hex "A" to hex "F"}. Up to 12 or 24 digits can be contained in a
single or double precision operand, respectively; the second word of a double holds the
low order digits. Depending on the operator, the digit sequence is left- or right-justified
within the operand. The extension is not used.
Boolean Operands
Some operators generate and other operators consume operands interpreted as Boolean
values. The Boolean values true and false are represented as binary 1 and 0,
respectively. The terms True and False are used to specify Boolean values. In the
specification of a stack output from an operator, True and False are defined as the 1-bit
integer values 1 and 0, respectively. In the specification of a stack argument for an
operator, True and False are defined as operands with bit [0:1] equal to 1 or 0,
respectively; Boolean interpretation ignores field [47:47] of any operand, the extension,
and the second word of a double precision operand.
Boolean operands are generated by the relational operators, among others. Operands are
interpreted as Boolean values by the branch operators and Assert operators. The logical
operators do not interpret Boolean values; rather, they perform Boolean arithmetic on
the argument bit vectors.
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