Vodafone SS 08 - Manual (Page 39)

TU Dresden, 4/29/2008 Slide 39
chair
Numerical Issues - 32-bit Multiplication
ƒ It is possible to perform 32-bit multiplication
using 16-bit multipliers.
ƒ Example: c = a x b (with 32-bit values).
a a
h h
a a
l l
b b
h h
b b
l l
a = a =
b = b =
32 32 - - bits bits
a * b = (a
h
<< 16 + a
l
)* (b
h
<< 16 + b
l
)
= [(a
h
* b
h
) << 32] + [(a
l
* b
h
) << 16] +
[(a
h
* b
l
) << 16] + [a
l
* b
l
]