Stores the index in a binary file. * IMPORTANT NOTE: The set of data points is NOT stored in the file, so * when loading the index object

wuffs_base__color_u32_argb_premul__as__color_u64_argb_nonpremul converts from 4x8 premultiplied alpha to 4x16LE non-premultiplied alpha.

wuffs_base__io_writer__limited_copy_u32_from_history_8_byte_chunks_distance_1_fast copies the previous byte (the one immediately before *ptr_iop_w), c

TGA doesn't start with a magic identifier. Instead, see if the opening bytes are plausibly TGA. Callers should have already verified that (prefix_dat

wuffs_base__multiply_u64 returns x*y as a 128-bit value. The maximum inclusive output hi_lo is 0xFFFFFFFFFFFFFFFE_0000000000000001.

wuffs_base__pixel_buffer__palette returns the palette color data. If non-empty, it will have length WUFFS_BASE__PIXEL_FORMAT__INDEXED__PALETTE_BYTE_LE

wuffs_base__status__message strips the leading '$', '#' or '@'.

Assume pixel format is FLOAT for all channels.