From 8832e728d362992a38eef89613b44d24f18e6c2a Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 2 Oct 2025 09:29:31 +0200 Subject: [PATCH] varint: reimplement as test balloon for Rust Implement a trivial test balloon for our Rust build infrastructure by reimplementing the "varint.c" subsystem in Rust. This subsystem is chosen because it is trivial to convert and because it doesn't have any dependencies to other components of Git. If support for Rust is enabled, we stop compiling "varint.c" and instead compile and use "src/varint.rs". Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- Makefile | 3 ++ meson.build | 5 ++- src/lib.rs | 1 + src/meson.build | 1 + src/varint.rs | 92 +++++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 101 insertions(+), 1 deletion(-) create mode 100644 src/varint.rs diff --git a/Makefile b/Makefile index 31e79342e1..2a7fc5cb1f 100644 --- a/Makefile +++ b/Makefile @@ -1307,7 +1307,9 @@ LIB_OBJS += urlmatch.o LIB_OBJS += usage.o LIB_OBJS += userdiff.o LIB_OBJS += utf8.o +ifndef WITH_RUST LIB_OBJS += varint.o +endif LIB_OBJS += version.o LIB_OBJS += versioncmp.o LIB_OBJS += walker.o @@ -1499,6 +1501,7 @@ CLAR_TEST_OBJS += $(UNIT_TEST_DIR)/unit-test.o UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o RUST_SOURCES += src/lib.rs +RUST_SOURCES += src/varint.rs GIT-VERSION-FILE: FORCE @OLD=$$(cat $@ 2>/dev/null || :) && \ diff --git a/meson.build b/meson.build index 234a9e9d6f..37dfa28601 100644 --- a/meson.build +++ b/meson.build @@ -522,7 +522,6 @@ libgit_sources = [ 'usage.c', 'userdiff.c', 'utf8.c', - 'varint.c', 'version.c', 'versioncmp.c', 'walker.c', @@ -1707,6 +1706,10 @@ rust_option = get_option('rust').disable_auto_if(not cargo.found()) if rust_option.allowed() subdir('src') libgit_c_args += '-DWITH_RUST' +else + libgit_sources += [ + 'varint.c', + ] endif libgit = declare_dependency( diff --git a/src/lib.rs b/src/lib.rs index e69de29bb2..9da70d8b57 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -0,0 +1 @@ +pub mod varint; diff --git a/src/meson.build b/src/meson.build index c8d874b210..25b9ad5a14 100644 --- a/src/meson.build +++ b/src/meson.build @@ -1,5 +1,6 @@ libgit_rs_sources = [ 'lib.rs', + 'varint.rs', ] # Unfortunately we must use a wrapper command to move the output file into the diff --git a/src/varint.rs b/src/varint.rs new file mode 100644 index 0000000000..6e610bdd8e --- /dev/null +++ b/src/varint.rs @@ -0,0 +1,92 @@ +#[no_mangle] +pub unsafe extern "C" fn decode_varint(bufp: *mut *const u8) -> u64 { + let mut buf = *bufp; + let mut c = *buf; + let mut val = u64::from(c & 127); + + buf = buf.add(1); + + while (c & 128) != 0 { + val = val.wrapping_add(1); + if val == 0 || val.leading_zeros() < 7 { + return 0; // overflow + } + + c = *buf; + buf = buf.add(1); + + val = (val << 7) + u64::from(c & 127); + } + + *bufp = buf; + val +} + +#[no_mangle] +pub unsafe extern "C" fn encode_varint(value: u64, buf: *mut u8) -> u8 { + let mut varint: [u8; 16] = [0; 16]; + let mut pos = varint.len() - 1; + + varint[pos] = (value & 127) as u8; + + let mut value = value >> 7; + while value != 0 { + pos -= 1; + value -= 1; + varint[pos] = 128 | (value & 127) as u8; + value >>= 7; + } + + if !buf.is_null() { + std::ptr::copy_nonoverlapping(varint.as_ptr().add(pos), buf, varint.len() - pos); + } + + (varint.len() - pos) as u8 +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn test_decode_varint() { + unsafe { + assert_eq!(decode_varint(&mut [0x00].as_slice().as_ptr()), 0); + assert_eq!(decode_varint(&mut [0x01].as_slice().as_ptr()), 1); + assert_eq!(decode_varint(&mut [0x7f].as_slice().as_ptr()), 127); + assert_eq!(decode_varint(&mut [0x80, 0x00].as_slice().as_ptr()), 128); + assert_eq!(decode_varint(&mut [0x80, 0x01].as_slice().as_ptr()), 129); + assert_eq!(decode_varint(&mut [0x80, 0x7f].as_slice().as_ptr()), 255); + + // Overflows are expected to return 0. + assert_eq!(decode_varint(&mut [0x88; 16].as_slice().as_ptr()), 0); + } + } + + #[test] + fn test_encode_varint() { + unsafe { + let mut varint: [u8; 16] = [0; 16]; + + assert_eq!(encode_varint(0, std::ptr::null_mut()), 1); + + assert_eq!(encode_varint(0, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [0; 16]); + + assert_eq!(encode_varint(10, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(127, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [127, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(128, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(129, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(255, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 127, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + } + } +}