feat(zseri): Add store-ref-scanner crate

This crate implements the scanner for finding references to store
paths in uncompressed binary blobs and text files.
It is currently a minimally working prototype and
it is probably a good idea to polish the interface further.

Change-Id: I8406f9d52d254fc3d660ea2b9bc9b7841cc815ec
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4596
Tested-by: BuildkiteCI
Reviewed-by: zseri <zseri.devel@ytrizja.de>

users/zseri/store-ref-scanner/src/hbm.rs

@@ -0,0 +1,150 @@
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct HalfBytesMask(pub [u8; 16]);
+
+impl HalfBytesMask {
+    pub const B32_REVSHA256: HalfBytesMask =
+        HalfBytesMask([0, 0, 0, 0, 0, 0, 255, 3, 0, 0, 0, 0, 222, 127, 207, 7]);
+
+    pub const B64_BLAKE2B256: HalfBytesMask = HalfBytesMask([
+        0, 0, 0, 0, 0, 8, 255, 3, 254, 255, 255, 135, 254, 255, 255, 7,
+    ]);
+
+    #[inline]
+    #[proc_unroll::unroll]
+    pub const fn from_expanded(x: [bool; 128]) -> Self {
+        let mut ret = [0u8; 16];
+        for idx in 0..16 {
+            let mut tmp = 0;
+            let fin = idx * 8;
+            macro_rules! bitx {
+            ($($a:expr),+) => {{ $( if x[fin + $a] { tmp += (1 << $a) as u8; } )+ }}
+            }
+            bitx!(0, 1, 2, 3, 4, 5, 6, 7);
+            ret[idx] = tmp;
+        }
+        Self(ret)
+    }
+
+    /// create a mask by allowing all characters via the mask which are included in the given string
+    pub fn from_bytes(s: &[u8]) -> Self {
+        s.iter().fold(Self([0u8; 16]), |mut ret, &i| {
+            ret.set(i, true);
+            ret
+        })
+    }
+
+    #[proc_unroll::unroll]
+    pub const fn into_expanded(self) -> [bool; 128] {
+        let Self(ihbm) = self;
+        let mut ret = [false; 128];
+        for idx in 0..16 {
+            let fin = idx * 8;
+            let curi = ihbm[idx];
+            macro_rules! bitx {
+                ($($a:expr),+) => {{ $( ret[fin + $a] = (curi >> $a) & 0b1 != 0; )+ }}
+            }
+            bitx!(0, 1, 2, 3, 4, 5, 6, 7);
+        }
+        ret
+    }
+
+    pub fn contains(&self, byte: u8) -> bool {
+        (self.0[usize::from(byte / 8)] >> u32::from(byte % 8)) & 0b1 != 0
+    }
+
+    pub fn set(&mut self, byte: u8, allow: bool) {
+        if byte >= 0x80 {
+            if cfg!(debug_assertions) {
+                panic!(
+                    "tried to manipulate invalid byte {:?} in HalfBytesMask",
+                    byte
+                );
+            } else {
+                return;
+            }
+        }
+        let mut block = &mut self.0[usize::from(byte / 8)];
+        let bitpat = (1 << u32::from(byte % 8)) as u8;
+        if allow {
+            *block |= bitpat;
+        } else {
+            *block &= !bitpat;
+        }
+    }
+
+    #[cfg(test)]
+    fn count_ones(&self) -> u8 {
+        self.0
+            .iter()
+            .map(|i| i.count_ones())
+            .sum::<u32>()
+            .try_into()
+            .unwrap()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn maskbase() {
+        assert_eq!(HalfBytesMask::B32_REVSHA256.count_ones(), 32);
+        assert_eq!(HalfBytesMask::B64_BLAKE2B256.count_ones(), 64);
+    }
+
+    #[test]
+    fn dflmask() {
+        assert_eq!(
+            HalfBytesMask::from_expanded(
+                [
+                    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,
+                ]
+                .map(|i| i != 0)
+            ),
+            Default::default(),
+        );
+
+        assert_eq!(
+            HalfBytesMask::from_expanded(
+                [
+                    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, 1, 1, 1, 1,
+                    1, 1, 1, 1, 1, 1, 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, 1, 1, 1, 1, 0, 1, 1,
+                    1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,
+                ]
+                .map(|i| i != 0)
+            ),
+            HalfBytesMask::B32_REVSHA256,
+        );
+
+        assert_eq!(
+            HalfBytesMask::from_expanded(
+                [
+                    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, 1, 0, 0, 0, 0, 1, 1, 1, 1,
+                    1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+                    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1,
+                    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,
+                ]
+                .map(|i| i != 0)
+            ),
+            HalfBytesMask::B64_BLAKE2B256,
+        );
+    }
+
+    proptest::proptest! {
+        #[test]
+        fn hbm_roundtrip(s: [u8; 16]) {
+            let a = HalfBytesMask(s);
+            let b = a.into_expanded();
+            let c = HalfBytesMask::from_expanded(b);
+            assert_eq!(a, c);
+        }
+    }
+}