Sign-extend and duplicate 16 bit values in Toit using blit

extend_blit.toit

import bitmap show blit
import expect show *

/**
Takes a byte array of little endian 16 bit values.
Returns a new byte array of little endian 32 bit values, sign extended.
For each input 16 bit value there are two (copied) 32 bit output values.
*/
expand input/ByteArray -> ByteArray:
  output := ByteArray input.size * 4
  // Sign extend.
  2.repeat:
    blit input[1..] output[2 + it..] input.size / 2
        --source_pixel_stride=2
        --destination_pixel_stride=8
        --lookup_table=SIGN_EXTEND_TABLE
  // Expand.
  blit input output 2
      --destination_line_stride=8
  // Duplicate the 32 bit values.
  blit output output[4..] 4
      --source_line_stride=8
      --destination_line_stride=8

  return output

test in/ByteArray expect/ByteArray -> none:
  output := expand in
  expect_equals output expect

main:
  test #[0, 0] #[0, 0, 0, 0, 0, 0, 0, 0]
  test #[4, 0] #[4, 0, 0, 0, 4, 0, 0, 0]
  test #[4, 255] #[4, 255, 255, 255, 4, 255, 255, 255]
  test #[4, 255, 3, 5] #[4, 255, 255, 255, 4, 255, 255, 255, 3, 5, 0, 0, 3, 5, 0, 0]

SIGN_EXTEND_TABLE ::= #[
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255]