Cray CRAY-1 - Floating Point Multiply Unit

Floating point multiply unit
The floating point multiply unit executes instructions 064 through 067
and 160 through 167. These instructions provide for full and half
precision multiplication of 64-bit operands in floating point format and
for computing two minus a floating point product for reciprocal iterations.
The half-precision product is rounded; the full-precision product is
either rounded or unrounded.
Input operands are
assumed to be normalized. The unit delivers a
normalized
result except that the result is not guaranteed to be
I correct if the input operands are not normalized.
I
Out-of-range exponents are detected as described under Floating Point
Arithmetic. However, if both operands have zero exponents, the result
is considered as an integer product and is not normalized.
Functional unit time
is seven clock periods.
Reciprocal approximation
unit
The reciprocal approximation unit finds the approximate reciprocal of a
64-bit operand in floating point format. The unit executes instructions
070 and 174. If the Vector Population Instructions Option is installed,
the k field must be a for the reciprocal approximation instruction, 174,
to
be recognized. Functional unit time is 14 clock periods.
The result is normalized. The input operand is assumed to be normalized;
the uppermost
bit of the coefficient is not tested but is assumed to be
set in the computation.
2240004
3-19
E