RCA Spectra 70 - Page 220

Notes
(Cont'd)
Floating-P oint I
nstr'Uctions
For long operands, the intermediate sum consists of fourteen hexa-
decimal digits
and a possible carry. No guard digit is retained.
2.
After addition, the intermediate sum is left-shifted until all high-
order zero hexadecimal digits have been eliminated. The vacated
low-order digits are made zero and the exponent is decremented by
one for each zero digit shifted. If no left-shift takes place, the inter-
mediate sum is truncated to the proper mantissa length. If the
exponent underflows (exceeds - 64) during normalization, the float-
ing-point
number is made true zero and an exponent underflow
interrupt occurs.
3. No normalization is
performed when the intermediate sum is zero.
The sum mantissa is unaltered and a significance error interrupt
occurs. If a significance error interrupt is prohibited by the interrupt
mask, the quantity is made true zero and a significance error
interrupt does not occur.
4.
Initial operands need not be in normalized form.
5. The sign of the sum is determined by the rules of algebra. A zero
sum is always plus.
6.
Short operands do not alter the low-order halves of the registers
specified by the address fields.
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