`nx_crc32_v1.nx` source

1// crc32.nx -- CRC-32 checksum (IEEE 802.3 + Castagnoli).
2//
3// Two widely-used variants:
4//
5//   crc32    IEEE 802.3 polynomial 0xEDB88320 (reversed).
6//            Used by: ZIP, PNG, gzip, Ethernet, PNG, Adler (old TCP).
7//
8//   crc32c   Castagnoli polynomial 0x82F63B78 (reversed).
9//            Used by: iSCSI, SCTP, ZFS, BTRFS, Google Wire Format,
10//            AWS S3 checksum-algorithm-CRC32C.  Better error
11//            detection + hardware-accelerated on x86 (CRC32Q op)
12//            and ARMv8.
13//
14// Not cryptographic -- trivial to forge.  Good only as an integrity
15// check against random bit-flips (storage, transmission).
16//
17// Algorithm: table-less bit-by-bit variant.  8 iterations per input
18// byte; each iteration xor-shifts the current CRC by 1 and
19// conditionally xors in the polynomial.  ~50 CPU cycles per byte;
20// for high-throughput callers, a future 256-entry table lookup
21// lands when NishiLang gets proper const-array literals.
22//
23// Both variants start with CRC = 0xFFFFFFFF and end by xor'ing
24// with 0xFFFFFFFF (i.e., complement) -- matches every reference
25// implementation (zlib, CRC-32/BZIP2 identical handling).
26//
27// Invariants:
28//   CRC1  Output is exact match for zlib's crc32() / crc32c() for
29//         the same input.  Known-answer: crc32("") = 0x00000000;
30//         crc32("123456789") = 0xCBF43926; crc32c("123456789") =
31//         0xE3069283.
32//   CRC2  Input read-only; returns u32 result packed into the low
33//         32 bits of i64.
34//   CRC3  No branch on data: the "conditionally xor" is a mask-
35//         multiply (0 or 1 times polynomial) -- not secret-time
36//         critical (CRC isn't crypto) but keeps the loop shape
37//         predictable.
38
39// nx_safety_envelope:
40//   intended_use:       AUTO_APPLIED -- primitive-specific tuning queued
41//   sil_target:         SIL1
42//   evidence:           [bulk_applied_2026-05-16, see-file-comment-for-detail]
43//   verdict:            NOT_YET_EVALUATED
44
45import "nx_syscalls.nx"
46
47const CRC32_POLY:  i64 = 0xEDB88320
48const CRC32C_POLY: i64 = 0x82F63B78
49const U32_MASK:    i64 = 0xFFFFFFFF
50const U32_INIT:    i64 = 0xFFFFFFFF
51
52// Core bit-by-bit CRC loop.  Parameterised by polynomial so both
53// crc32 and crc32c share the kernel.
54func crc32_core(poly: i64, bytes: *u8, n: i64, initial: i64) -> i64 {
55    var crc: i64 = initial
56    var i: i64 = 0
57    while i < n {
58        crc = crc ^ bytes[i]
59        var bit: i64 = 0
60        while bit < 8 {
61            let lsb: i64 = crc & 1
62            let mask: i64 = 0 - lsb       // 0 or all-ones
63            crc = ((crc >> 1) & 0x7FFFFFFFFFFFFFFF) ^ (mask & poly)
64            // NishiLang >> on i64 is arithmetic; mask high bits
65            // above 32 to keep the CRC a true u32.
66            crc = crc & U32_MASK
67            bit = bit + 1
68        }
69        i = i + 1
70    }
71    return crc & U32_MASK
72}
73
74// IEEE 802.3 / zlib CRC-32.
75func crc32(bytes: *u8, n: i64) -> i64 {
76    let raw: i64 = crc32_core(CRC32_POLY, bytes, n, U32_INIT)
77    return (raw ^ U32_INIT) & U32_MASK
78}
79
80// Castagnoli CRC-32C.
81func crc32c(bytes: *u8, n: i64) -> i64 {
82    let raw: i64 = crc32_core(CRC32C_POLY, bytes, n, U32_INIT)
83    return (raw ^ U32_INIT) & U32_MASK
84}
85
86// Compile-only smoke.  Known answer crc32("123456789") = 0xCBF43926
87// from RFC 3720.  We can't verify the numeric output without
88// execution; structure-check is what we have today.
89func main() -> i64 {
90    let msg: *u8 = "123456789"
91    let c1: i64 = crc32(msg, 9)
92    let c2: i64 = crc32c(msg, 9)
93    // Return xor of the two -- nonzero if they differ (they
94    // should; different polynomials).
95    if c1 == c2 { return 1 }
96    return 0
97}
nx_crc32_v1.nx source

`nx_crc32_v1.nx` source
