Difference between revisions of "Instruction Set/mask"

Revision as of 10:46, 19 January 2015

Convert between bitmasks and bool vectors.

The lowest width bits of a bitmask become the element bool values of a new vector, or the bool element values of a vector become the new bits in a bitmask, depending on whether the input operand is a scalar or a vector.

mask(bit bit0, bit bit1, width w) → op r0

This doesn't work with vectors at all. It doesn't even have belt operands. It is rather a way to produce a class of often used constant values that usually would take a lot of space as a normal manifest constant.

The values produced by mask are bitmasks: A sequence of ones in an otherwise empty bitfield, or a sequence of zeros in an otherwise filled bitfield.

The two bit paramters are the start and stop bit indices, i.e. the greater value is the highest order bit that is part of the sequence, and the lower value is the highest order bit not part of the sequence anymore. When the greater value is first, it is a series of ones within zeros, when it is second, it is a series of zeros within ones.

mask(op v, width w) → op r0

The width determines how many bits or elements are used from the operand. The bool vector conversion mask operation has one of the more complicated operand masks. This is because the direction of the conversion, vector to bitmask or vice versa, depends on the scalarity Metadata.
So from this perspective it isn't that complicated at all: bitmasks produce bool vectors, and bool vectors produce bitmasks.

Instruction Set, alphabetical, Instruction Set by Category, Instruction Set, sortable, filterable