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

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

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

get status

initialize a callback-based context

initialize a memory-decode context

Safe Cast Helper for size_t ==> int

if there's a pending marker from the entropy stream, return that otherwise, fetch from the stream and get a marker. if there's no marker, return 0xff,

returns 1 if the product is valid, 0 on overflow. negative factors are considered invalid.