1 files changed, 93 insertions, 0 deletions
diff --git a/lib/std/debug/FixedBufferReader.zig b/lib/std/debug/FixedBufferReader.zig
new file mode 100644
index 0000000000..494245a9e9
--- /dev/null
+++ b/lib/std/debug/FixedBufferReader.zig
@@ -0,0 +1,93 @@
+//! Optimized for performance in debug builds.
+
+const std = @import("../std.zig");
+const MemoryAccessor = std.debug.MemoryAccessor;
+
+const FixedBufferReader = @This();
+
+buf: []const u8,
+pos: usize = 0,
+endian: std.builtin.Endian,
+
+pub const Error = error{ EndOfBuffer, Overflow, InvalidBuffer };
+
+pub fn seekTo(fbr: *FixedBufferReader, pos: u64) Error!void {
+    if (pos > fbr.buf.len) return error.EndOfBuffer;
+    fbr.pos = @intCast(pos);
+}
+
+pub fn seekForward(fbr: *FixedBufferReader, amount: u64) Error!void {
+    if (fbr.buf.len - fbr.pos < amount) return error.EndOfBuffer;
+    fbr.pos += @intCast(amount);
+}
+
+pub inline fn readByte(fbr: *FixedBufferReader) Error!u8 {
+    if (fbr.pos >= fbr.buf.len) return error.EndOfBuffer;
+    defer fbr.pos += 1;
+    return fbr.buf[fbr.pos];
+}
+
+pub fn readByteSigned(fbr: *FixedBufferReader) Error!i8 {
+    return @bitCast(try fbr.readByte());
+}
+
+pub fn readInt(fbr: *FixedBufferReader, comptime T: type) Error!T {
+    const size = @divExact(@typeInfo(T).Int.bits, 8);
+    if (fbr.buf.len - fbr.pos < size) return error.EndOfBuffer;
+    defer fbr.pos += size;
+    return std.mem.readInt(T, fbr.buf[fbr.pos..][0..size], fbr.endian);
+}
+
+pub fn readIntChecked(
+    fbr: *FixedBufferReader,
+    comptime T: type,
+    ma: *MemoryAccessor,
+) Error!T {
+    if (ma.load(T, @intFromPtr(fbr.buf[fbr.pos..].ptr)) == null)
+        return error.InvalidBuffer;
+
+    return fbr.readInt(T);
+}
+
+pub fn readUleb128(fbr: *FixedBufferReader, comptime T: type) Error!T {
+    return std.leb.readUleb128(T, fbr);
+}
+
+pub fn readIleb128(fbr: *FixedBufferReader, comptime T: type) Error!T {
+    return std.leb.readIleb128(T, fbr);
+}
+
+pub fn readAddress(fbr: *FixedBufferReader, format: std.dwarf.Format) Error!u64 {
+    return switch (format) {
+        .@"32" => try fbr.readInt(u32),
+        .@"64" => try fbr.readInt(u64),
+    };
+}
+
+pub fn readAddressChecked(
+    fbr: *FixedBufferReader,
+    format: std.dwarf.Format,
+    ma: *MemoryAccessor,
+) Error!u64 {
+    return switch (format) {
+        .@"32" => try fbr.readIntChecked(u32, ma),
+        .@"64" => try fbr.readIntChecked(u64, ma),
+    };
+}
+
+pub fn readBytes(fbr: *FixedBufferReader, len: usize) Error![]const u8 {
+    if (fbr.buf.len - fbr.pos < len) return error.EndOfBuffer;
+    defer fbr.pos += len;
+    return fbr.buf[fbr.pos..][0..len];
+}
+
+pub fn readBytesTo(fbr: *FixedBufferReader, comptime sentinel: u8) Error![:sentinel]const u8 {
+    const end = @call(.always_inline, std.mem.indexOfScalarPos, .{
+        u8,
+        fbr.buf,
+        fbr.pos,
+        sentinel,
+    }) orelse return error.EndOfBuffer;
+    defer fbr.pos = end + 1;
+    return fbr.buf[fbr.pos..end :sentinel];
+}