jpeg-decoder 0.1.18

// Malicious JPEG files can cause operations in the idct to overflow.
// One example is tests/crashtest/images/imagetestsuite/b0b8914cc5f7a6eff409f16d8cc236c5.jpg
// That's why wrapping operators are needed.
use crate::parser::Dimensions;

pub(crate) fn choose_idct_size(full_size: Dimensions, requested_size: Dimensions) -> usize {
    fn scaled(len: u16, scale: usize) -> u16 { ((len as u32 * scale as u32 - 1) / 8 + 1) as u16 }

    for &scale in &[1, 2, 4] {
        if scaled(full_size.width, scale) >= requested_size.width || scaled(full_size.height, scale) >= requested_size.height {
            return scale;
        }
    }

    return 8;
}

#[test]
fn test_choose_idct_size() {
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 200, height: 200}), 1);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 500, height: 500}), 1);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 684, height: 456}), 1);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 999, height: 456}), 1);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 684, height: 999}), 1);
    assert_eq!(choose_idct_size(Dimensions{width: 500, height: 333}, Dimensions{width: 63, height: 42}), 1);

    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 685, height: 999}), 2);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 1000, height: 1000}), 2);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 1400, height: 1400}), 4);
    
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 5472, height: 3648}), 8);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 16384, height: 16384}), 8);
    assert_eq!(choose_idct_size(Dimensions{width: 1, height: 1}, Dimensions{width: 65535, height: 65535}), 8);
    assert_eq!(choose_idct_size(Dimensions{width: 5472, height: 3648}, Dimensions{width: 16384, height: 16384}), 8);
}

pub(crate) fn dequantize_and_idct_block(scale: usize, coefficients: &[i16], quantization_table: &[u16; 64], output_linestride: usize, output: &mut [u8]) {
    match scale {
        8 => dequantize_and_idct_block_8x8(coefficients, quantization_table, output_linestride, output),
        4 => dequantize_and_idct_block_4x4(coefficients, quantization_table, output_linestride, output),
        2 => dequantize_and_idct_block_2x2(coefficients, quantization_table, output_linestride, output),
        1 => dequantize_and_idct_block_1x1(coefficients, quantization_table, output_linestride, output),
        _ => panic!("Unsupported IDCT scale {}/8", scale),
    }
}

// This is based on stb_image's 'stbi__idct_block'.
fn dequantize_and_idct_block_8x8(coefficients: &[i16], quantization_table: &[u16; 64], output_linestride: usize, output: &mut [u8]) {
    debug_assert_eq!(coefficients.len(), 64);

    let mut temp = [0i32; 64];

    // columns
    for i in 0 .. 8 {
        // if all zeroes, shortcut -- this avoids dequantizing 0s and IDCTing
        if coefficients[i + 8] == 0 && coefficients[i + 16] == 0 && coefficients[i + 24] == 0 &&
                coefficients[i + 32] == 0 && coefficients[i + 40] == 0 && coefficients[i + 48] == 0 &&
                coefficients[i + 56] == 0 {
            let dcterm = (coefficients[i] as i32 * quantization_table[i] as i32).wrapping_shl(2);
            temp[i]      = dcterm;
            temp[i + 8]  = dcterm;
            temp[i + 16] = dcterm;
            temp[i + 24] = dcterm;
            temp[i + 32] = dcterm;
            temp[i + 40] = dcterm;
            temp[i + 48] = dcterm;
            temp[i + 56] = dcterm;
        }
        else {
            let s0 = coefficients[i] as i32      * quantization_table[i] as i32;
            let s1 = coefficients[i + 8] as i32  * quantization_table[i + 8] as i32;
            let s2 = coefficients[i + 16] as i32 * quantization_table[i + 16] as i32;
            let s3 = coefficients[i + 24] as i32 * quantization_table[i + 24] as i32;
            let s4 = coefficients[i + 32] as i32 * quantization_table[i + 32] as i32;
            let s5 = coefficients[i + 40] as i32 * quantization_table[i + 40] as i32;
            let s6 = coefficients[i + 48] as i32 * quantization_table[i + 48] as i32;
            let s7 = coefficients[i + 56] as i32 * quantization_table[i + 56] as i32;

            let p2 = s2;
            let p3 = s6;
            let p1 = p2.wrapping_add(p3).wrapping_mul(stbi_f2f(0.5411961));
            let t2 = p1.wrapping_add(p3.wrapping_mul(stbi_f2f(-1.847759065)));
            let t3 = p1.wrapping_add(p2.wrapping_mul(stbi_f2f(0.765366865)));
            let p2 = s0;
            let p3 = s4;
            let t0 = stbi_fsh(p2.wrapping_add(p3));
            let t1 = stbi_fsh(p2.wrapping_sub(p3));
            let x0 = t0.wrapping_add(t3);
            let x3 = t0.wrapping_sub(t3);
            let x1 = t1.wrapping_add(t2);
            let x2 = t1.wrapping_sub(t2);
            let t0 = s7;
            let t1 = s5;
            let t2 = s3;
            let t3 = s1;
            let p3 = t0.wrapping_add(t2);
            let p4 = t1.wrapping_add(t3);
            let p1 = t0.wrapping_add(t3);
            let p2 = t1.wrapping_add(t2);
            let p5 = p3.wrapping_add(p4).wrapping_mul(stbi_f2f(1.175875602));
            let t0 = t0.wrapping_mul(stbi_f2f(0.298631336));
            let t1 = t1.wrapping_mul(stbi_f2f(2.053119869));
            let t2 = t2.wrapping_mul(stbi_f2f(3.072711026));
            let t3 = t3.wrapping_mul(stbi_f2f(1.501321110));
            let p1 = p5.wrapping_add(p1.wrapping_mul(stbi_f2f(-0.899976223)));
            let p2 = p5.wrapping_add(p2.wrapping_mul(stbi_f2f(-2.562915447)));
            let p3 = p3.wrapping_mul(stbi_f2f(-1.961570560));
            let p4 = p4.wrapping_mul(stbi_f2f(-0.390180644));
            let t3 = t3.wrapping_add(p1.wrapping_add(p4));
            let t2 = t2.wrapping_add(p2.wrapping_add(p3));
            let t1 = t1.wrapping_add(p2.wrapping_add(p4));
            let t0 = t0.wrapping_add(p1.wrapping_add(p3));

            // constants scaled things up by 1<<12; let's bring them back
            // down, but keep 2 extra bits of precision
            let x0 = x0.wrapping_add(512);
            let x1 = x1.wrapping_add(512);
            let x2 = x2.wrapping_add(512);
            let x3 = x3.wrapping_add(512);

            temp[i]      = x0.wrapping_add(t3).wrapping_shr(10);
            temp[i + 56] = x0.wrapping_sub(t3).wrapping_shr(10);
            temp[i + 8]  = x1.wrapping_add(t2).wrapping_shr(10);
            temp[i + 48] = x1.wrapping_sub(t2).wrapping_shr(10);
            temp[i + 16] = x2.wrapping_add(t1).wrapping_shr(10);
            temp[i + 40] = x2.wrapping_sub(t1).wrapping_shr(10);
            temp[i + 24] = x3.wrapping_add(t0).wrapping_shr(10);
            temp[i + 32] = x3.wrapping_sub(t0).wrapping_shr(10);
        }
    }

    for i in 0 .. 8 {
        // no fast case since the first 1D IDCT spread components out
        let s0 = temp[i * 8];
        let s1 = temp[i * 8 + 1];
        let s2 = temp[i * 8 + 2];
        let s3 = temp[i * 8 + 3];
        let s4 = temp[i * 8 + 4];
        let s5 = temp[i * 8 + 5];
        let s6 = temp[i * 8 + 6];
        let s7 = temp[i * 8 + 7];

        let p2 = s2;
        let p3 = s6;
        let p1 = p2.wrapping_add(p3).wrapping_mul(stbi_f2f(0.5411961));
        let t2 = p1.wrapping_add(p3.wrapping_mul(stbi_f2f(-1.847759065)));
        let t3 = p1.wrapping_add(p2.wrapping_mul(stbi_f2f(0.765366865)));
        let p2 = s0;
        let p3 = s4;
        let t0 = stbi_fsh(p2.wrapping_add(p3));
        let t1 = stbi_fsh(p2.wrapping_sub(p3));
        let x0 = t0.wrapping_add(t3);
        let x3 = t0.wrapping_sub(t3);
        let x1 = t1.wrapping_add(t2);
        let x2 = t1.wrapping_sub(t2);
        let t0 = s7;
        let t1 = s5;
        let t2 = s3;
        let t3 = s1;
        let p3 = t0.wrapping_add(t2);
        let p4 = t1.wrapping_add(t3);
        let p1 = t0.wrapping_add(t3);
        let p2 = t1.wrapping_add(t2);
        let p5 = p3.wrapping_add(p4).wrapping_mul(stbi_f2f(1.175875602));
        let t0 = t0.wrapping_mul(stbi_f2f(0.298631336));
        let t1 = t1.wrapping_mul(stbi_f2f(2.053119869));
        let t2 = t2.wrapping_mul(stbi_f2f(3.072711026));
        let t3 = t3.wrapping_mul(stbi_f2f(1.501321110));
        let p1 = p5.wrapping_add(p1.wrapping_mul(stbi_f2f(-0.899976223)));
        let p2 = p5.wrapping_add(p2.wrapping_mul(stbi_f2f(-2.562915447)));
        let p3 = p3.wrapping_mul(stbi_f2f(-1.961570560));
        let p4 = p4.wrapping_mul(stbi_f2f(-0.390180644));
        let t3 = t3.wrapping_add(p1.wrapping_add(p4));
        let t2 = t2.wrapping_add(p2.wrapping_add(p3));
        let t1 = t1.wrapping_add(p2.wrapping_add(p4));
        let t0 = t0.wrapping_add(p1.wrapping_add(p3));

        // constants scaled things up by 1<<12, plus we had 1<<2 from first
        // loop, plus horizontal and vertical each scale by sqrt(8) so together
        // we've got an extra 1<<3, so 1<<17 total we need to remove.
        // so we want to round that, which means adding 0.5 * 1<<17,
        // aka 65536. Also, we'll end up with -128 to 127 that we want
        // to encode as 0..255 by adding 128, so we'll add that before the shift
        let x0 = x0.wrapping_add(65536 + (128 << 17));
        let x1 = x1.wrapping_add(65536 + (128 << 17));
        let x2 = x2.wrapping_add(65536 + (128 << 17));
        let x3 = x3.wrapping_add(65536 + (128 << 17));

        output[i * output_linestride]     = stbi_clamp(x0.wrapping_add(t3).wrapping_shr(17));
        output[i * output_linestride + 7] = stbi_clamp(x0.wrapping_sub(t3).wrapping_shr(17));
        output[i * output_linestride + 1] = stbi_clamp(x1.wrapping_add(t2).wrapping_shr(17));
        output[i * output_linestride + 6] = stbi_clamp(x1.wrapping_sub(t2).wrapping_shr(17));
        output[i * output_linestride + 2] = stbi_clamp(x2.wrapping_add(t1).wrapping_shr(17));
        output[i * output_linestride + 5] = stbi_clamp(x2.wrapping_sub(t1).wrapping_shr(17));
        output[i * output_linestride + 3] = stbi_clamp(x3.wrapping_add(t0).wrapping_shr(17));
        output[i * output_linestride + 4] = stbi_clamp(x3.wrapping_sub(t0).wrapping_shr(17));
    }
}

// 4x4 and 2x2 IDCT based on Rakesh Dugad and Narendra Ahuja: "A Fast Scheme for Image Size Change in the Compressed Domain" (2001).
// http://sylvana.net/jpegcrop/jidctred/
fn dequantize_and_idct_block_4x4(coefficients: &[i16], quantization_table: &[u16; 64], output_linestride: usize, output: &mut [u8]) {
    debug_assert_eq!(coefficients.len(), 64);
    let mut temp = [0i32; 4*4];

    const CONST_BITS: u32 = 12;
    const PASS1_BITS: u32 = 2;
    const FINAL_BITS: u32 = CONST_BITS + PASS1_BITS + 3;

    // columns
    for i in 0 .. 4 {
        let s0 = coefficients[i + 8*0] as i32 * quantization_table[i + 8*0] as i32;
        let s1 = coefficients[i + 8*1] as i32 * quantization_table[i + 8*1] as i32;
        let s2 = coefficients[i + 8*2] as i32 * quantization_table[i + 8*2] as i32;
        let s3 = coefficients[i + 8*3] as i32 * quantization_table[i + 8*3] as i32;
    
        let x0 = s0.wrapping_add(s2).wrapping_shl(PASS1_BITS);
        let x2 = s0.wrapping_sub(s2).wrapping_shl(PASS1_BITS);

        let p1 = s1.wrapping_add(s3).wrapping_mul(stbi_f2f(0.541196100));
        let t0 = p1.wrapping_add(s3.wrapping_mul(stbi_f2f(-1.847759065))).wrapping_add(512).wrapping_shr(CONST_BITS - PASS1_BITS);
        let t2 = p1.wrapping_add(s1.wrapping_mul(stbi_f2f( 0.765366865))).wrapping_add(512).wrapping_shr(CONST_BITS - PASS1_BITS);

        temp[i + 4*0] = x0.wrapping_add(t2);
        temp[i + 4*3] = x0.wrapping_sub(t2);
        temp[i + 4*1] = x2.wrapping_add(t0);
        temp[i + 4*2] = x2.wrapping_sub(t0);
    }

    for i in 0 .. 4 {
        let s0 = temp[i * 4 + 0];
        let s1 = temp[i * 4 + 1];
        let s2 = temp[i * 4 + 2];
        let s3 = temp[i * 4 + 3];

        let x0 = s0.wrapping_add(s2).wrapping_shl(CONST_BITS);
        let x2 = s0.wrapping_sub(s2).wrapping_shl(CONST_BITS);

        let p1 = s1.wrapping_add(s3).wrapping_mul(stbi_f2f(0.541196100));
        let t0 = p1.wrapping_add(s3.wrapping_mul(stbi_f2f(-1.847759065)));
        let t2 = p1.wrapping_add(s1.wrapping_mul(stbi_f2f(0.765366865)));

        // constants scaled things up by 1<<12, plus we had 1<<2 from first
        // loop, plus horizontal and vertical each scale by sqrt(8) so together
        // we've got an extra 1<<3, so 1<<17 total we need to remove.
        // so we want to round that, which means adding 0.5 * 1<<17,
        // aka 65536. Also, we'll end up with -128 to 127 that we want
        // to encode as 0..255 by adding 128, so we'll add that before the shift
        let x0 = x0.wrapping_add((1 << (FINAL_BITS - 1)) + (128 << FINAL_BITS));
        let x2 = x2.wrapping_add((1 << (FINAL_BITS - 1)) + (128 << FINAL_BITS));

        output[i * output_linestride + 0] = stbi_clamp(x0.wrapping_add(t2).wrapping_shr(FINAL_BITS));
        output[i * output_linestride + 3] = stbi_clamp(x0.wrapping_sub(t2).wrapping_shr(FINAL_BITS));
        output[i * output_linestride + 1] = stbi_clamp(x2.wrapping_add(t0).wrapping_shr(FINAL_BITS));
        output[i * output_linestride + 2] = stbi_clamp(x2.wrapping_sub(t0).wrapping_shr(FINAL_BITS));
    }
}

fn dequantize_and_idct_block_2x2(coefficients: &[i16], quantization_table: &[u16; 64], output_linestride: usize, output: &mut [u8]) {
    debug_assert_eq!(coefficients.len(), 64);

    const SCALE_BITS: u32 = 3;

    // Column 0
    let s00 = coefficients[8*0] as i32 * quantization_table[8*0] as i32;
    let s10 = coefficients[8*1] as i32 * quantization_table[8*1] as i32;

    let x0 = s00.wrapping_add(s10);
    let x2 = s00.wrapping_sub(s10);

    // Column 1
    let s01 = coefficients[8*0+1] as i32 * quantization_table[8*0+1] as i32;
    let s11 = coefficients[8*1+1] as i32 * quantization_table[8*1+1] as i32;

    let x1 = s01.wrapping_add(s11);
    let x3 = s01.wrapping_sub(s11);

    let x0 = x0.wrapping_add((1 << (SCALE_BITS-1)) + (128 << SCALE_BITS));
    let x2 = x2.wrapping_add((1 << (SCALE_BITS-1)) + (128 << SCALE_BITS));

    // Row 0
    output[0] = stbi_clamp(x0.wrapping_add(x1).wrapping_shr(SCALE_BITS));
    output[1] = stbi_clamp(x0.wrapping_sub(x1).wrapping_shr(SCALE_BITS));

    // Row 1
    output[output_linestride + 0] = stbi_clamp(x2.wrapping_add(x3).wrapping_shr(SCALE_BITS));
    output[output_linestride + 1] = stbi_clamp(x2.wrapping_sub(x3).wrapping_shr(SCALE_BITS));
}

fn dequantize_and_idct_block_1x1(coefficients: &[i16], quantization_table: &[u16; 64], _output_linestride: usize, output: &mut [u8]) {
    debug_assert_eq!(coefficients.len(), 64);

    let s0 = (coefficients[0] as i32 * quantization_table[0] as i32).wrapping_add(128 * 8) / 8;
    output[0] = stbi_clamp(s0);
}

// take a -128..127 value and stbi__clamp it and convert to 0..255
fn stbi_clamp(x: i32) -> u8
{
   // trick to use a single test to catch both cases
   if x as u32 > 255 {
      if x < 0 { return 0; }
      if x > 255 { return 255; }
   }

   x as u8
}

fn stbi_f2f(x: f32) -> i32 {
    (x * 4096.0 + 0.5) as i32
}

fn stbi_fsh(x: i32) -> i32 {
    x << 12
}