Fix/no std feature (currently wasm compatible; groundwork for no_std)

.github/workflows/tests.yml

@@ -25,17 +25,17 @@ jobs:
           components: rustfmt, clippy
           cache-key: ${{ matrix.os }}-${{ matrix.rust-toolchain }}
       - name: Check
-        run: cargo check
+        run: cargo check --all-features
       - name: Architecture check
-        run: cargo run --bin arch-check
+        run: cargo run --features cli --bin arch-check
       - if: ${{ matrix.rust-toolchain != 'nightly' }}
         name: Format
         run: cargo fmt -- --check
       - if: ${{ matrix.rust-toolchain != 'nightly' }}
         name: Clippy
-        run: cargo clippy
+        run: cargo clippy --all-features
       - name: Test
-        run: cargo test
+        run: cargo test --features cli
 
   test-x86_64:
     name: Test x86_64
@@ -56,17 +56,17 @@ jobs:
           components: rustfmt, clippy
           cache-key: ${{ matrix.os }}-${{ matrix.rust-toolchain }}
       - name: Check
-        run: cargo check
+        run: cargo check --all-features
       - name: Architecture check
-        run: cargo run --bin arch-check
+        run: cargo run --features cli --bin arch-check
       - if: ${{ matrix.rust-toolchain != 'nightly' }}
         name: Format
         run: cargo fmt -- --check
       - if: ${{ matrix.rust-toolchain != 'nightly' }}
         name: Clippy
-        run: cargo clippy
+        run: cargo clippy --all-features
       - name: Test
-        run: cargo test
+        run: cargo test --features cli
 
   test-x86:
     name:  Test x86
@@ -88,11 +88,11 @@ jobs:
       - name: Set up cross
         run: cargo install cross --locked --version 0.2.5
       - name: Check
-        run: cross check --target ${{ matrix.target }}
+        run: cross check --all-features --target ${{ matrix.target }}
       - name: Architecture check
-        run: cross run --bin arch-check --target ${{ matrix.target }}
+        run: cross run --features cli --bin arch-check --target ${{ matrix.target }}
       - name: Test
-        run: cross test --target ${{ matrix.target }}
+        run: cross test --features cli --target ${{ matrix.target }}
 
   test-software:
     name: Test software fallback
@@ -114,8 +114,8 @@ jobs:
       - name: Set up cross
         run: cargo install cross --locked --version 0.2.5
       - name: Check
-        run: cross check --target ${{ matrix.target }}
+        run: cross check --all-features --target ${{ matrix.target }}
       - name: Architecture check
-        run: cross run --bin arch-check --target ${{ matrix.target }}
+        run: cross run --features cli --bin arch-check --target ${{ matrix.target }}
       - name: Test
-        run: cross test --target ${{ matrix.target }}
+        run: cross test --features cli --target ${{ matrix.target }}

Cargo.toml

@@ -24,8 +24,6 @@ bench = true
 [dependencies]
 crc = "3"
 digest = {  version = "0.10", features = ["alloc"] }
-rand = "0.9"
-regex = "1.12"
 
 # will be removed once Rust 1.89 is the minimum supported version
 rustversion = "1.0"
@@ -36,6 +34,8 @@ indexmap = { version = ">=2.11.0, <2.12.0", optional = true }
 [dev-dependencies]
 criterion = "0.7"
 cbindgen = "0.29"
+rand = "0.9"
+regex = "1.12"
 
 # lto=true has a big improvement in performance
 [profile.release]
@@ -44,11 +44,29 @@ strip = true
 codegen-units = 1
 opt-level = 3
 
+[[bin]]
+name = "checksum"
+path = "src/bin/checksum.rs"
+required-features = ["cli"]
+
+[[bin]]
+name = "arch-check"
+path = "src/bin/arch-check.rs"
+required-features = ["cli"]
+
+[[bin]]
+name = "get-custom-params"
+path = "src/bin/get-custom-params.rs"
+required-features = ["cli"]
+
 [[bench]]
 name = "benchmark"
 harness = false
 
 [features]
+default = ["std"]
+std = []
+cli = ["std"]
 alloc = []
 
 # the features below are deprecated, aren't in use, and will be removed in the next MAJOR version (v2)
@@ -60,4 +78,13 @@ optimize_crc32_neon_v3s4x2e_v2 = [] # deprecated
 optimize_crc32_neon_blended = [] # deprecated
 optimize_crc32_avx512_vpclmulqdq_v3x2 = [] # deprecated
 optimize_crc32_avx512_v4s3x3 = [] # deprecated
-optimize_crc32_sse_v4s3x3 = [] # deprecated
+optimize_crc32_sse_v4s3x3 = [] # deprecated
+
+[package.metadata.docs.rs]
+features = ["std"]
+rustdoc-args = ["--cfg", "docsrs"]
+
+[[test]]
+name = "checksum_integration_tests"
+path = "tests/checksum_integration_tests.rs"
+required-features = ["cli"]

src/bin/checksum.rs

@@ -3,7 +3,6 @@
 //! This is a simple program to calculate a checksum from the command line
 
 use crc_fast::{checksum, checksum_file, CrcAlgorithm};
-use rand::RngCore;
 use std::env;
 use std::process::ExitCode;
 use std::str::FromStr;
@@ -151,6 +150,22 @@ impl BenchmarkResult {
     }
 }
 
+/// Fills a buffer with pseudo-random data using xorshift64* algorithm.
+/// This is a deterministic PRNG that's tiny, fast, and suitable for benchmark data generation.
+/// The seed is derived from the buffer size to provide some variability.
+/// This solves the problem of having to use a full-featured PRNG like rand for benchmark data generation.
+#[inline]
+fn fill_pseudo_random(buf: &mut [u8], seed: u64) {
+    let mut x = seed;
+    for b in buf {
+        x ^= x >> 12;
+        x ^= x << 25;
+        x ^= x >> 27;
+        let r = x.wrapping_mul(0x2545_F491_4F6C_DD1D);
+        *b = r as u8;
+    }
+}
+
 fn generate_random_data(size: usize) -> Result<Vec<u8>, String> {
     // Check for reasonable size limits to prevent memory issues
     if size > 1_073_741_824 {
@@ -160,8 +175,11 @@ fn generate_random_data(size: usize) -> Result<Vec<u8>, String> {
 
     // Use vec! macro to avoid clippy warning about slow initialization
     let mut buf = vec![0u8; size];
-    let mut rng = rand::rng();
-    rng.fill_bytes(&mut buf);
+
+    // Derive seed from size for deterministic but varied data
+    let seed = 0x9E37_79B9_7F4A_7C15_u64.wrapping_add(size as u64);
+    fill_pseudo_random(&mut buf, seed);
+
     Ok(buf)
 }
 

src/lib.rs

@@ -1,4 +1,6 @@
 // Copyright 2025 Don MacAskill. Licensed under MIT or Apache-2.0.
+// Future proofing for no_std support
+#![cfg_attr(not(feature = "std"), no_std)]
 
 //! `crc-fast`
 //! ===========
@@ -144,7 +146,10 @@ use crate::crc64::consts::{
 use crate::structs::Calculator;
 use crate::traits::CrcCalculator;
 use digest::{DynDigest, InvalidBufferSize};
+
+#[cfg(feature = "std")]
 use std::fs::File;
+#[cfg(feature = "std")]
 use std::io::{Read, Write};
 
 mod algorithm;
@@ -545,6 +550,7 @@ impl Digest {
     }
 }
 
+#[cfg(feature = "std")]
 impl Write for Digest {
     #[inline(always)]
     fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
@@ -643,6 +649,7 @@ pub fn checksum_with_params(params: CrcParams, buf: &[u8]) -> u64 {
 ///
 /// assert_eq!(checksum.unwrap(), 0xcbf43926);
 /// ```
+#[cfg(feature = "std")]
 #[inline(always)]
 pub fn checksum_file(
     algorithm: CrcAlgorithm,
@@ -685,6 +692,7 @@ pub fn checksum_file(
 ///
 /// assert_eq!(checksum.unwrap(), 0xcbf43926);
 /// ```
+#[cfg(feature = "std")]
 pub fn checksum_file_with_params(
     params: CrcParams,
     path: &str,
@@ -698,6 +706,7 @@ pub fn checksum_file_with_params(
 /// # Errors
 ///
 /// This function will return an error if the file cannot be read.
+#[cfg(feature = "std")]
 fn checksum_file_with_digest(
     mut digest: Digest,
     path: &str,

tests/checksum_integration_tests.rs

@@ -1,12 +1,24 @@
 // Copyright 2025 Don MacAskill. Licensed under MIT or Apache-2.0.
 
+#![cfg(feature = "cli")]
+
 use std::fs;
 use std::process::Command;
 
 #[test]
 fn test_benchmark_flag_parsing() {
     let output = Command::new("cargo")
-        .args(&["run", "--bin", "checksum", "--", "-a", "CRC-32/ISCSI", "-b"])
+        .args(&[
+            "run",
+            "--features",
+            "cli",
+            "--bin",
+            "checksum",
+            "--",
+            "-a",
+            "CRC-32/ISCSI",
+            "-b",
+        ])
         .output()
         .expect("Failed to execute command");
 
@@ -25,6 +37,8 @@ fn test_benchmark_with_size_parameter() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -47,6 +61,8 @@ fn test_benchmark_with_duration_parameter() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -69,6 +85,8 @@ fn test_benchmark_invalid_size() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -91,6 +109,8 @@ fn test_benchmark_invalid_duration() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -117,6 +137,8 @@ fn test_benchmark_with_file_input() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -144,6 +166,8 @@ fn test_benchmark_with_string_input() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -171,6 +195,8 @@ fn test_benchmark_different_algorithms() {
         let output = Command::new("cargo")
             .args(&[
                 "run",
+                "--features",
+                "cli",
                 "--bin",
                 "checksum",
                 "--",
@@ -198,6 +224,8 @@ fn test_benchmark_size_without_benchmark_flag() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",
@@ -219,6 +247,8 @@ fn test_benchmark_nonexistent_file() {
     let output = Command::new("cargo")
         .args(&[
             "run",
+            "--features",
+            "cli",
             "--bin",
             "checksum",
             "--",