Initial project import

tools/v/vlib/hash/adler32/adler32.v

@@ -0,0 +1,51 @@
+// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+// This is a pure V implementation of Adler-32 from RFC 1950.
+// Parameters: BASE=65521, init=1, output=(s2 << 16) | s1.
+module adler32
+
+// base is the largest prime smaller than 2^16, mandated by RFC 1950.
+pub const base = u32(65521)
+// nmax is the largest chunk size that keeps intermediate sums inside u32.
+// See RFC 1950 Appendix and zlib's adler32 implementation.
+pub const nmax = 5552
+
+// update_state updates an Adler-32 state with `data`.
+// For RFC-1950 compliant checksums, use state `1` for a new stream.
+@[direct_array_access]
+pub fn update_state(state u32, data []u8) u32 {
+	mut s1 := state & u32(0xffff)
+	mut s2 := state >> 16
+	mut pos := 0
+	for pos < data.len {
+		block_len := if data.len - pos > nmax { nmax } else { data.len - pos }
+		for _ in 0 .. block_len {
+			s1 += data[pos]
+			if s1 >= base {
+				s1 -= base
+			}
+			s2 += s1
+			pos++
+		}
+		s2 %= base
+	}
+	return (s2 << 16) | s1
+}
+
+// checksum returns the RFC-1950 Adler-32 checksum for `data`.
+pub fn checksum(data []u8) u32 {
+	return update_state(u32(1), data)
+}
+
+// update extends an existing Adler-32 checksum `adler` with `data`.
+// Use `adler = 1` for a fresh checksum.
+pub fn update(adler u32, data []u8) u32 {
+	return update_state(adler, data)
+}
+
+// sum is an alias for checksum.
+pub fn sum(data []u8) u32 {
+	return checksum(data)
+}