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

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

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.

decode a jpeg huffman value from the bitstream

after a restart interval, stbi__jpeg_reset the entropy decoder and the dc prediction

initialize a callback-based context