Cray CRAY-1 - Page 65

I
2-
1
(MULTIPLICAND)
2-
21
\
I~------~~--------------------------------------~
k >."
(MULTIPLIER)
1 h = 1 for half-precision round
2
f = 1 for full-precision round
3 Truncation
constant
hh
CD
A-OI03A
Figure 3-5. F.P. multiply partial product sums pyramid
The multiplication is commutative, that is, A times B equals B times A.
In a full-precision rounded multiply, 2 round bits are entered into the
·d t bOt °to 2-
50
d 2-
51
d 11 d t t th
pyraml a 1 POSl lon an an a owe 0 propaga e up e
pyramid.
For a half preclslon multiply, round bits are entered into the pyramid at
bit positions 2-32 and 2-31. A carry resulting from this entry is allowed
to propagate
up and a 30-bit result (2-
1
to 2-30) is transmitted back.
2240004
3-26 through 3-29 E-01