at94k10al ATMEL Corporation, at94k10al Datasheet - Page 116

• Manufacturer Part Number: at94k10al
• Description: At94k05al 5k - 40k Gates Of At40k Fpga With 8-bit Microcontroller, Up To 36k Bytes Of Sram And On-chip Jtag Ice
• Manufacturer: ATMEL Corporation

4.28.3
116
AT94KAL Series FPSLIC
16-bit x 16-bit = 16-bit Operation
This operation is valid for both unsigned and signed numbers, even though only the unsigned
multiply instruction (MUL) is needed, see
When A and B are positive numbers, or at least one of them is zero, the algorithm is clearly cor-
rect, provided that the product C = A • B is less than 2
unsigned number, or less than 2
When both factors are negative, the two’s complement notation is used:
A = 2
C = A • B = (2
Here we are only concerned with the 16 LSBs; the last part of this sum will be discarded and we
will get the (correct) result C = |A • B|.
Figure 4-38. 16-bit Multiplication, 16-bit Result
When one factor is negative and one factor is positive, for example, A is negative and B is
positive:
C = A • B = (2
The MSBs will be discarded and the correct two’s complement notation result will be
C = 2
The product must be in the range 0 ≤ C ≤ 2
2
When doing integer multiplication in C language, this is how it is done. The algorithm can be
expanded to do 32-bit multiplication with 32-bit result.
15
≤ C ≤ 2
16
16
- |A| and B = 2
- |A • B|.
15
- 1 if signed numbers are used.
16
16
- |A|) • (2
- |A|) • |B| = (2
16
- |B|:
16
- |B|) = |A • B| + 2
AH AL
+
+
=
16
15
• |B|) - |A • B| = (2
if the product is to be used as a signed number.
16
Figure
AL * BH
AH * BL
X
- 1 if unsigned numbers are used, and in the range -
32
- 2
4-38. A mathematical explanation is given:
CH
BH BL
AL * BL
16
16
• (|A| + |B|)
- |A • B|) + 2
CL
16
if the product is to be used as an
16
• (|B| - 1)
1
2
3
1138I–FPSLI–1/08