The Int64ShllMod32 function performs a left logical shift operation on an unsigned 64-bit integer value. The function provides improved shifting code for left logical shifts where the shift count is in the range 0 - 31.
DWORDLONG Int64ShllMod32(
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DWORDLONG Value, |
// specifies unsigned 64-bit integer to shift left logically |
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DWORD ShiftCount |
// specifies a shift count in the range 0 - 31 |
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); |
The return value is the unsigned 64-bit integer result of the left logical shift operation.
The shift count is the number of bit positions that the value’s bits move.
In a left logical shift operation on an unsigned value, the value’s bits move to the left, and vacated bits on the right side of the value are set to zero.
A compiler can generate optimal code for a left logical shift operation when the shift count is a constant. However, if the shift count is a variable whose range of values is unknown, the compiler must assume the worst case, leading to non-optimal code: code that calls a subroutine, or code that is inline but branches. By restricting the shift count to the range 0 - 31, the Int64ShllMod32 function lets the compiler generate optimal or near-optimal code.
Please note that the Int64ShllMod32 function’s Value parameter and return value are 64-bit values, not LARGE_INTEGER structures.