this is a weird definition of log2() for which log2(1) = 1, log2(2) = 2, log2(4) = 3 as required by the specification. fast(?) implementation from stb

update selection and cursor to match each other

fast 0..255 * 0..255 => 0..255 rounded multiplication

used in setup, and for huffman that doesn't go fast path

different grad function from Perlin's, but easy to modify to match reference

define ceil from floor

take a -128..127 value and stbi__clamp it and convert to 0..255

returns 1 if "a*b*c + add" has no negative terms/factors and doesn't overflow

INFINITE

initialize a callback-based context

initialize a memory-decode context

For perf reasons this code is duplicated in stbir__resample_horizontal_upsample/downsample, if you change it here change it there too.

Adds statistics srcInfo into inoutInfo, like: inoutInfo += srcInfo.

necessary to call this when using volatile to order writes/reads