Other Strength Reduction Operations
-
- This material is disputed. It is better described as peephole optimizations and instruction assignment.
Operator strength reduction uses mathematical identities to replace slow math operations with faster operations. The benefits depend on the target CPU and sometimes on the surrounding code (which can affect the availability of other functional units within the CPU).
- replacing integer division or multiplication by a power of 2 with an arithmetic shift or logical shift
- replacing integer multiplication by a constant with a combination of shifts, adds or subtracts
- replacing integer division by a constant with a multiplication, taking advantage of the limited range of machine integers.
| original calculation | replacement calculation |
|---|---|
| y = x / 8 | y = x >> 3 |
| y = x * 64 | y = x << 6 |
| y = x * 2 | y = x << 1 |
| y = x * 15 | y = (x << 4) - x |
Read more about this topic: Strength Reduction
Famous quotes containing the words strength, reduction and/or operations:
“One reason writers write is out of revenge. Life hurts; certain ideas and experiences hurt; one wants to clarify, to set out illuminations, to replay the old bad scenes and get the Treppenworte said—the words one didn’t have the strength or ripeness to say when those words were necessary for one’s dignity or survival.”
—Cynthia Ozick (b. 1928)
“The reduction of nuclear arsenals and the removal of the threat of worldwide nuclear destruction is a measure, in my judgment, of the power and strength of a great nation.”
—Jimmy Carter (James Earl Carter, Jr.)
“Plot, rules, nor even poetry, are not half so great beauties in tragedy or comedy as a just imitation of nature, of character, of the passions and their operations in diversified situations.”
—Horace Walpole (1717–1797)