Difference between revisions of "Embedded Programming Tips and Tricks"
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===Fast Division=== | ===Fast Division=== | ||
| − | + | On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right. | |
Each shift does a divide by two. | Each shift does a divide by two. | ||
| + | |||
For example | For example | ||
| − | |||
Y = Y >> 1 Will result in a divide by 2 | Y = Y >> 1 Will result in a divide by 2 | ||
| − | + | or | |
X = X >> 4 Will result in a divide by 16 | X = X >> 4 Will result in a divide by 16 | ||
| − | |||
By adding a multiplication you can achieve other, more complex, divisions. | By adding a multiplication you can achieve other, more complex, divisions. | ||
For example | For example | ||
| − | |||
Z = Z * 3; | Z = Z * 3; | ||
Z = Z >> 4; (div 16) | Z = Z >> 4; (div 16) | ||
| − | |||
Will result in a division of 5.33 (16/3 = 5.33) | Will result in a division of 5.33 (16/3 = 5.33) | ||
Revision as of 22:35, 12 November 2011
Fast Division
On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right. Each shift does a divide by two.
For example Y = Y >> 1 Will result in a divide by 2 or X = X >> 4 Will result in a divide by 16
By adding a multiplication you can achieve other, more complex, divisions.
For example Z = Z * 3; Z = Z >> 4; (div 16)
Will result in a division of 5.33 (16/3 = 5.33)
Be sure to do the multiply first, otherwise bits will be lost. Also be sure the variable size is large enough to store the multiplied value.
