Repository: mrhooray/crc-rs (language: rust)

Issue:
Latest commit (479783b165f39db94e97cff3432855f5a3cc07f2) broke IEEE checksum, at least. 
I unfortunately lack time for a full repro right now, but maybe this will help. This code:
 ```rust
        let crc = u32::from_le_bytes(data[0..CRC_SIZE].try_into().map_err(|_| Error::DataSize)?);
        let computed_crc = crc32::checksum_ieee(&data[DATA_START..]);

        if crc != computed_crc {
            return Err(Error::Crc);
        }
```
works right before that commit, but hits the error case after it. 


Discussion / hints:
See #52 for a possible reproduction of this issue.
thanks for the repro. +@akhilles 
Looks like the new crc table generation code doesn't compute the 255th element in the table:

```
[0, 1996959894, 3993919788, 2567524794, 124634137, 1886057615, 3915621685, 2657392035, 249268274, 2044508324, 3772115230, 2547177864, 162941995, 2125561021, 3887607047, 2428444049, 498536548, 1789927666, 4089016648, 2227061214, 450548861, 1843258603, 4107580753, 2211677639, 325883990, 1684777152, 4251122042, 2321926636, 335633487, 1661365465, 4195302755, 2366115317, 997073096, 1281953886, 3579855332, 2724688242, 1006888145, 1258607687, 3524101629, 2768942443, 901097722, 1119000684, 3686517206, 2898065728, 853044451, 1172266101, 3705015759, 2882616665, 651767980, 1373503546, 3369554304, 3218104598, 565507253, 1454621731, 3485111705, 3099436303, 671266974, 1594198024, 3322730930, 2970347812, 795835527, 1483230225, 3244367275, 3060149565, 1994146192, 31158534, 2563907772, 4023717930, 1907459465, 112637215, 2680153253, 3904427059, 2013776290, 251722036, 2517215374, 3775830040, 2137656763, 141376813, 2439277719, 3865271297, 1802195444, 476864866, 2238001368, 4066508878, 1812370925, 453092731, 2181625025, 4111451223, 1706088902, 314042704, 2344532202, 4240017532, 1658658271, 366619977, 2362670323, 4224994405, 1303535960, 984961486, 2747007092, 3569037538, 1256170817, 1037604311, 2765210733, 3554079995, 1131014506, 879679996, 2909243462, 3663771856, 1141124467, 855842277, 2852801631, 3708648649, 1342533948, 654459306, 3188396048, 3373015174, 1466479909, 544179635, 3110523913, 3462522015, 1591671054, 702138776, 2966460450, 3352799412, 1504918807, 783551873, 3082640443, 3233442989, 3988292384, 2596254646, 62317068, 1957810842, 3939845945, 2647816111, 81470997, 1943803523, 3814918930, 2489596804, 225274430, 2053790376, 3826175755, 2466906013, 167816743, 2097651377, 4027552580, 2265490386, 503444072, 1762050814, 4150417245, 2154129355, 426522225, 1852507879, 4275313526, 2312317920, 282753626, 1742555852, 4189708143, 2394877945, 397917763, 1622183637, 3604390888, 2714866558, 953729732, 1340076626, 3518719985, 2797360999, 1068828381, 1219638859, 3624741850, 2936675148, 906185462, 1090812512, 3747672003, 2825379669, 829329135, 1181335161, 3412177804, 3160834842, 628085408, 1382605366, 3423369109, 3138078467, 570562233, 1426400815, 3317316542, 2998733608, 733239954, 1555261956, 3268935591, 3050360625, 752459403, 1541320221, 2607071920, 3965973030, 1969922972, 40735498, 2617837225, 3943577151, 1913087877, 83908371, 2512341634, 3803740692, 2075208622, 213261112, 2463272603, 3855990285, 2094854071, 198958881, 2262029012, 4057260610, 1759359992, 534414190, 2176718541, 4139329115, 1873836001, 414664567, 2282248934, 4279200368, 1711684554, 285281116, 2405801727, 4167216745, 1634467795, 376229701, 2685067896, 3608007406, 1308918612, 956543938, 2808555105, 3495958263, 1231636301, 1047427035, 2932959818, 3654703836, 1088359270, 936918000, 2847714899, 3736837829, 1202900863, 817233897, 3183342108, 3401237130, 1404277552, 615818150, 3134207493, 3453421203, 1423857449, 601450431, 3009837614, 3294710456, 1567103746, 711928724, 3020668471, 3272380065, 1510334235, 0]
```

This is because the recursive macro only executes 255 times, not 256! Incredibly, none of the existing test cases were affected by this.

This is a simple indexing issue, will submit fix shortly.

Fix patch:
diff --git a/src/crc16.rs b/src/crc16.rs
index 5463fd8..32587e0 100644
--- a/src/crc16.rs
+++ b/src/crc16.rs
@@ -4,9 +4,9 @@ pub use crate::util::make_table_crc16 as make_table;
 use crate::CalcType;
 
 pub const X25: u16 = 0x1021;
-const X25_TABLE: [u16; 256] = make_table(X25, true);
+pub const X25_TABLE: [u16; 256] = make_table(X25, true);
 pub const USB: u16 = 0x8005;
-const USB_TABLE: [u16; 256] = make_table(USB, true);
+pub const USB_TABLE: [u16; 256] = make_table(USB, true);
 
 /// `Digest` struct for CRC calculation
 /// - `table`: Calculation table generated from input parameters.
diff --git a/src/crc32.rs b/src/crc32.rs
index 79b4d61..692ecc7 100644
--- a/src/crc32.rs
+++ b/src/crc32.rs
@@ -4,11 +4,11 @@ pub use crate::util::make_table_crc32 as make_table;
 use crate::CalcType;
 
 pub const CASTAGNOLI: u32 = 0x1EDC6F41;
-const CASTAGNOLI_TABLE: [u32; 256] = make_table(CASTAGNOLI, true);
+pub const CASTAGNOLI_TABLE: [u32; 256] = make_table(CASTAGNOLI, true);
 pub const IEEE: u32 = 0x04C11DB7;
-const IEEE_TABLE: [u32; 256] = make_table(IEEE, true);
+pub const IEEE_TABLE: [u32; 256] = make_table(IEEE, true);
 pub const KOOPMAN: u32 = 0x741B8CD7;
-const KOOPMAN_TABLE: [u32; 256] = make_table(KOOPMAN, true);
+pub const KOOPMAN_TABLE: [u32; 256] = make_table(KOOPMAN, true);
 
 /// `Digest` struct for CRC calculation
 /// - `table`: Calculation table generated from input parameters.
diff --git a/src/crc64.rs b/src/crc64.rs
index 50054ec..8e814f1 100644
--- a/src/crc64.rs
+++ b/src/crc64.rs
@@ -4,9 +4,9 @@ pub use crate::util::make_table_crc64 as make_table;
 use crate::CalcType;
 
 pub const ECMA: u64 = 0x42F0E1EBA9EA3693;
-const ECMA_TABLE: [u64; 256] = make_table(ECMA, true);
+pub const ECMA_TABLE: [u64; 256] = make_table(ECMA, true);
 pub const ISO: u64 = 0x000000000000001B;
-const ISO_TABLE: [u64; 256] = make_table(ISO, true);
+pub const ISO_TABLE: [u64; 256] = make_table(ISO, true);
 
 /// `Digest` struct for CRC calculation
 /// - `table`: Calculation table generated from input parameters.
diff --git a/src/util.rs b/src/util.rs
index cd9cd09..56be8a4 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -5,14 +5,22 @@ macro_rules! repeat {
     );
 }
 
+macro_rules! repeat_i {
+    ($repeat_fn:expr, $input:expr, $count:expr,) => ($repeat_fn($input, $count));
+    ($repeat_fn:expr, $input:expr, $count:expr, a $($a:ident)*) => (
+        $repeat_fn(repeat_i!($repeat_fn, $input, $count + 1, $($a)*), $count)
+    );
+}
+
 /// Builds a CRC16 table using the standard or reflected method.
 /// If reflect==true, flip the individual byte bitwise, then flip the table value bitwise.
 pub const fn make_table_crc16(poly: u16, reflect: bool) -> [u16; 256] {
     let table = [0u16; 256];
-    let (_, _, _, table) = repeat!(
+    let (_, _, table) = repeat_i!(
         build_table_16,
-        (poly, reflect, 0, table),
-        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
+        (poly, reflect, table),
+        0u8, 
+        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
@@ -27,10 +35,11 @@ pub const fn make_table_crc16(poly: u16, reflect: bool) -> [u16; 256] {
 /// Builds a CRC32 table using the standard or reflected method.
 pub const fn make_table_crc32(poly: u32, reflect: bool) -> [u32; 256] {
     let table = [0u32; 256];
-    let (_, _, _, table) = repeat!(
+    let (_, _, table) = repeat_i!(
         build_table_32,
-        (poly, reflect, 0, table),
-        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
+        (poly, reflect, table),
+        0u8, 
+        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
@@ -45,10 +54,11 @@ pub const fn make_table_crc32(poly: u32, reflect: bool) -> [u32; 256] {
 /// Builds a CRC64 table using the standard or reflected method.
 pub const fn make_table_crc64(poly: u64, reflect: bool) -> [u64; 256] {
     let table = [0u64; 256];
-    let (_, _, _, table) = repeat!(
+    let (_, _, table) = repeat_i!(
         build_table_64,
-        (poly, reflect, 0, table),
-        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
+        (poly, reflect, table),
+        0u8, 
+        a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
         a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
@@ -60,8 +70,8 @@ pub const fn make_table_crc64(poly: u64, reflect: bool) -> [u64; 256] {
     table
 }
 
-pub const fn build_table_16((poly, reflect, i, mut table): (u16, bool, u8, [u16; 256])) -> (u16, bool, u8, [u16; 256]) {
-    let byte = [i, reflect_byte(i)][reflect as usize] as u16;
+pub const fn build_table_16((poly, reflect, mut table): (u16, bool, [u16; 256]), i: u8) -> (u16, bool, [u16; 256]) {
+    let byte = [i, reflect_8(i)][reflect as usize] as u16;
 
     // Shift the current table value "i" to the top byte in the long
     let value: u16 = byte << 8;
@@ -71,13 +81,13 @@ pub const fn build_table_16((poly, reflect, i, mut table): (u16, bool, u8, [u16;
         a a a a a a a
     );
 
-    value = [value, reflect_value_16(value)][reflect as usize];
+    value = [value, reflect_16(value)][reflect as usize];
     table[i as usize] = value;
-    (poly, reflect, i + 1, table)
+    (poly, reflect, table)
 }
 
-pub const fn build_table_32((poly, reflect, i, mut table): (u32, bool, u8, [u32; 256])) -> (u32, bool, u8, [u32; 256]) {
-    let byte = [i, reflect_byte(i)][reflect as usize] as u32;
+pub const fn build_table_32((poly, reflect, mut table): (u32, bool, [u32; 256]), i: u8) -> (u32, bool, [u32; 256]) {
+    let byte = [i, reflect_8(i)][reflect as usize] as u32;
 
     // Shift the current table value "i" to the top byte in the long
     let value: u32 = byte << 24;
@@ -87,13 +97,13 @@ pub const fn build_table_32((poly, reflect, i, mut table): (u32, bool, u8, [u32;
         a a a a a a a
     );
 
-    value = [value, reflect_value_32(value)][reflect as usize];
+    value = [value, reflect_32(value)][reflect as usize];
     table[i as usize] = value;
-    (poly, reflect, i + 1, table)
+    (poly, reflect, table)
 }
 
-pub const fn build_table_64((poly, reflect, i, mut table): (u64, bool, u8, [u64; 256])) -> (u64, bool, u8, [u64; 256]) {
-    let byte = [i, reflect_byte(i)][reflect as usize] as u64;
+pub const fn build_table_64((poly, reflect, mut table): (u64, bool, [u64; 256]), i: u8) -> (u64, bool, [u64; 256]) {
+    let byte = [i, reflect_8(i)][reflect as usize] as u64;
 
     // Shift the current table value "i" to the top byte in the long
     let value: u64 = byte << 56;
@@ -103,9 +113,9 @@ pub const fn build_table_64((poly, reflect, i, mut table): (u64, bool, u8, [u64;
         a a a a a a a
     );
 
-    value = [value, reflect_value_64(value)][reflect as usize];
+    value = [value, reflect_64(value)][reflect as usize];
     table[i as usize] = value;
-    (poly, reflect, i + 1, table)
+    (poly, reflect, table)
 }
 
 pub const fn poly_sum_16((poly, value): (u16, u16)) -> (u16, u16) {
@@ -120,30 +130,36 @@ pub const fn poly_sum_64((poly, value): (u64, u64)) -> (u64, u64) {
     (poly, (value << 1) ^ ((value >> 63) * poly))
 }
 
-const fn reflect_byte(mut b: u8) -> u8 {
+const fn reflect_8(mut b: u8) -> u8 {
     b = (b & 0xF0) >> 4 | (b & 0x0F) << 4;
     b = (b & 0xCC) >> 2 | (b & 0x33) << 2;
     b = (b & 0xAA) >> 1 | (b & 0x55) << 1;
     b
 }
 
-/// Reflects a value of a 16 bit number.
-const fn reflect_value_16(value: u16) -> u16 {
-    let l = (reflect_byte(value as u8) as u16) << 8;
-    let r = reflect_byte((value >> 8) as u8) as u16;
-    l | r
+const fn reflect_16(mut b: u16) -> u16 {
+    b = (b & 0xFF00) >> 8 | (b & 0x00FF) << 8;
+    b = (b & 0xF0F0) >> 4 | (b & 0x0F0F) << 4;
+    b = (b & 0xCCCC) >> 2 | (b & 0x3333) << 2;
+    b = (b & 0xAAAA) >> 1 | (b & 0x5555) << 1;
+    b
 }
 
-/// Reflects a value of a 32 bit number.
-const fn reflect_value_32(value: u32) -> u32 {
-    let l = (reflect_value_16(value as u16) as u32) << 16;
-    let r = reflect_value_16((value >> 16) as u16) as u32;
-    l | r
+const fn reflect_32(mut b: u32) -> u32 {
+    b = (b & 0xFFFF0000) >> 16 | (b & 0x0000FFFF) << 16;
+    b = (b & 0xFF00FF00) >> 8  | (b & 0x00FF00FF) << 8;
+    b = (b & 0xF0F0F0F0) >> 4  | (b & 0x0F0F0F0F) << 4;
+    b = (b & 0xCCCCCCCC) >> 2  | (b & 0x33333333) << 2;
+    b = (b & 0xAAAAAAAA) >> 1  | (b & 0x55555555) << 1;
+    b
 }
 
-/// Reflects a value of a 64 bit number.
-const fn reflect_value_64(value: u64) -> u64 {
-    let l = (reflect_value_32(value as u32) as u64) << 32;
-    let r = reflect_value_32((value >> 32) as u32) as u64;
-    l | r
+const fn reflect_64(mut b: u64) -> u64 {
+    b = (b & 0xFFFFFFFF00000000) >> 32 | (b & 0x00000000FFFFFFFF) << 32;
+    b = (b & 0xFFFF0000FFFF0000) >> 16 | (b & 0x0000FFFF0000FFFF) << 16;
+    b = (b & 0xFF00FF00FF00FF00) >> 8  | (b & 0x00FF00FF00FF00FF) << 8;
+    b = (b & 0xF0F0F0F0F0F0F0F0) >> 4  | (b & 0x0F0F0F0F0F0F0F0F) << 4;
+    b = (b & 0xCCCCCCCCCCCCCCCC) >> 2  | (b & 0x3333333333333333) << 2;
+    b = (b & 0xAAAAAAAAAAAAAAAA) >> 1  | (b & 0x5555555555555555) << 1;
+    b
 }


Test patch: