Editing Bit array (section)

=== Inversion ===

Vertical flipping of a one-bit-per-pixel image, or some FFT algorithms, requires flipping the bits of individual words (so <code>b31 b30 ... b0</code> becomes <code>b0 ... b30 b31</code>).
When this operation is not available on the processor, it's still possible to proceed by successive passes, in this example on 32 bits:

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exchange two 16-bit halfwords
exchange bytes by pairs (0xddccbbaa -> 0xccddaabb)
...
swap bits by pairs
swap bits (b31 b30 ... b1 b0 -> b30 b31 ... b0 b1)

The last operation can be written ((x&0x55555555) << 1) | (x&0xaaaaaaaa) >> 1)).
</syntaxhighlight>