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synced 2024-11-23 20:03:31 +01:00
hashx: Rust hook for inspecting and modifying the random number stream
This patch has no effect on the C tor build. Adds a function hashx_rng_callback() to the hashx API, defined only when HASHX_RNG_CALLBACK is defined. This is then used in the Rust wrapper to implement a similar rng_callback(). Included some minimal test cases. This code is intented for use in cross-compatibility fuzzing tests which drive multiple implementations of hashx with the same custom Rng stream. Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
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@ -9,7 +9,7 @@
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[package]
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name = "tor-c-equix"
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version = "0.1.0"
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version = "0.2.0"
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edition = "2021"
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license = "LGPL-3.0-only"
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@ -16,6 +16,8 @@ fn main() {
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"hashx/src/siphash_rng.c",
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"hashx/src/virtual_memory.c",
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])
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// Activate our patch for hashx_rng_callback
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.define("HASHX_RNG_CALLBACK", "1")
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// Equi-X always uses HashX size 8 (64-bit output)
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.define("HASHX_SIZE", "8")
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// Avoid shared library API declarations, link statically
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@ -31,6 +33,7 @@ fn main() {
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.header_contents(
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"wrapper.h",
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r#"
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#define HASHX_RNG_CALLBACK 1
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#define HASHX_SIZE 8
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#define HASHX_SHARED 1
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#define EQUIX_SHARED 1
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@ -169,6 +169,25 @@ HASHX_API hashx_result hashx_exec(const hashx_ctx* ctx,
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*/
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HASHX_API void hashx_free(hashx_ctx* ctx);
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#ifdef HASHX_RNG_CALLBACK
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/*
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* Set a callback for inspecting or modifying the HashX random number stream.
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*
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* The callback and its user pointer are associated with the provided context
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* even if it's re-used for another hash program. A callback value of NULL
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* disables the callback.
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*
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* @param ctx is pointer to a HashX instance.
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* @param callback is invoked after each new 64-bit pseudorandom value
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* is generated in a buffer. The callback may record it and/or replace
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* it. A NULL pointer here disables the callback.
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* @param user_data is an opaque parameter given to the callback
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*/
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HASHX_API void hashx_rng_callback(hashx_ctx* ctx,
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void (*callback)(uint64_t*, void*),
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void* user_data);
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#endif
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#ifdef __cplusplus
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}
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#endif
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@ -55,3 +55,13 @@ void hashx_free(hashx_ctx* ctx) {
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free(ctx);
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}
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}
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#ifdef HASHX_RNG_CALLBACK
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void hashx_rng_callback(hashx_ctx* ctx,
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void (*callback)(uint64_t*, void*),
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void* callback_user_data)
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{
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ctx->program.rng_callback = callback;
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ctx->program.rng_callback_user_data = callback_user_data;
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}
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#endif
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@ -554,6 +554,10 @@ bool hashx_program_generate(const siphash_state* key, hashx_program* program) {
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.ports = {{ 0 }}
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};
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hashx_siphash_rng_init(&ctx.gen, key);
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#ifdef HASHX_RNG_CALLBACK
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ctx.gen.callback = program->rng_callback;
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ctx.gen.callback_user_data = program->rng_callback_user_data;
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#endif
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for (int i = 0; i < 8; ++i) {
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ctx.registers[i].last_op = -1;
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ctx.registers[i].latency = 0;
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@ -29,6 +29,10 @@ typedef struct hashx_program {
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int branch_count;
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int branches[16];
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#endif
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#ifdef HASHX_RNG_CALLBACK
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void (*rng_callback)(uint64_t *buffer, void *user_data);
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void *rng_callback_user_data;
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#endif
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} hashx_program;
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#ifdef __cplusplus
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@ -15,6 +15,11 @@ uint8_t hashx_siphash_rng_u8(siphash_rng* gen) {
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gen->buffer8 = hashx_siphash13_ctr(gen->counter, &gen->keys);
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gen->counter++;
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gen->count8 = sizeof(gen->buffer8);
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#ifdef HASHX_RNG_CALLBACK
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if (gen->callback) {
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gen->callback(&gen->buffer8, gen->callback_user_data);
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}
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#endif
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}
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gen->count8--;
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return gen->buffer8 >> (gen->count8 * 8);
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@ -25,6 +30,11 @@ uint32_t hashx_siphash_rng_u32(siphash_rng* gen) {
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gen->buffer32 = hashx_siphash13_ctr(gen->counter, &gen->keys);
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gen->counter++;
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gen->count32 = sizeof(gen->buffer32) / sizeof(uint32_t);
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#ifdef HASHX_RNG_CALLBACK
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if (gen->callback) {
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gen->callback(&gen->buffer32, gen->callback_user_data);
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}
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#endif
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}
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gen->count32--;
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return (uint32_t)(gen->buffer32 >> (gen->count32 * 32));
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@ -13,6 +13,10 @@ typedef struct siphash_rng {
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uint64_t counter;
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uint64_t buffer8, buffer32;
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unsigned count8, count32;
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#ifdef HASHX_RNG_CALLBACK
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void (*callback)(uint64_t *buffer, void *user_data);
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void *callback_user_data;
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#endif
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} siphash_rng;
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#ifdef __cplusplus
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@ -12,6 +12,10 @@
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//! See `LICENSE` for licensing information.
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//!
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use core::ffi::c_void;
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use core::mem;
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use core::ptr::null_mut;
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pub mod ffi {
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//! Low-level access to the C API
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@ -34,8 +38,14 @@ pub const HASHX_SIZE: usize = ffi::HASHX_SIZE as usize;
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/// Output value obtained by executing a HashX hash function
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pub type HashXOutput = [u8; HASHX_SIZE];
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/// Type for callback functions that inspect or replace the pseudorandom stream
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pub type RngCallback = Box<dyn FnMut(u64) -> u64>;
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/// Safe wrapper around a HashX context
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pub struct HashX(*mut ffi::hashx_ctx);
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pub struct HashX {
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ctx: *mut ffi::hashx_ctx,
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rng_callback: Option<RngCallback>,
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}
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impl HashX {
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/// Allocate a new HashX context
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@ -44,7 +54,10 @@ impl HashX {
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if ctx.is_null() {
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panic!("out of memory in hashx_alloc");
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}
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Self(ctx)
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Self {
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ctx,
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rng_callback: None,
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}
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}
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/// Create a new hash function within this context, using the given seed
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@ -53,14 +66,15 @@ impl HashX {
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/// error occurs while the interpreter is disabled.
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#[inline(always)]
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pub fn make(&mut self, seed: &[u8]) -> HashXResult {
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unsafe { ffi::hashx_make(self.0, seed.as_ptr() as *const std::ffi::c_void, seed.len()) }
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unsafe { ffi::hashx_make(self.ctx, seed.as_ptr() as *const c_void, seed.len()) }
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}
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/// Check which implementation was selected by `make`
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#[inline(always)]
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pub fn query_type(&mut self) -> Result<HashXType, HashXResult> {
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let mut buffer = HashXType::HASHX_TYPE_INTERPRETED; // Arbitrary default
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let result = unsafe { ffi::hashx_query_type(self.0, &mut buffer as *mut ffi::hashx_type) };
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let result =
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unsafe { ffi::hashx_query_type(self.ctx, &mut buffer as *mut ffi::hashx_type) };
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match result {
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HashXResult::HASHX_OK => Ok(buffer),
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e => Err(e),
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@ -71,23 +85,45 @@ impl HashX {
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#[inline(always)]
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pub fn exec(&mut self, input: u64) -> Result<HashXOutput, HashXResult> {
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let mut buffer: HashXOutput = Default::default();
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let result = unsafe {
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ffi::hashx_exec(
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self.0,
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input,
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&mut buffer as *mut u8 as *mut std::ffi::c_void,
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)
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};
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let result =
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unsafe { ffi::hashx_exec(self.ctx, input, &mut buffer as *mut u8 as *mut c_void) };
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match result {
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HashXResult::HASHX_OK => Ok(buffer),
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e => Err(e),
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}
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}
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/// Set a callback function that may inspect and/or modify the internal
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/// pseudorandom number stream used by this context.
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///
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/// The function will be owned by this context, and it replaces any
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/// previous function that may have been set. Returns the previous callback
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/// if any.
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pub fn rng_callback(&mut self, callback: Option<RngCallback>) -> Option<RngCallback> {
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// Keep ownership of our Rust value in the context wrapper, to match
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// the lifetime of the mutable pointer that the C API saves.
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let result = mem::replace(&mut self.rng_callback, callback);
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match &mut self.rng_callback {
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None => unsafe { ffi::hashx_rng_callback(self.ctx, None, null_mut()) },
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Some(callback) => unsafe {
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ffi::hashx_rng_callback(
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self.ctx,
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Some(wrapper),
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callback as *mut RngCallback as *mut c_void,
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);
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},
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}
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unsafe extern "C" fn wrapper(buffer: *mut u64, callback: *mut c_void) {
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let callback: &mut RngCallback = unsafe { mem::transmute(callback) };
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buffer.write(callback(buffer.read()));
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}
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result
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}
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}
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impl Drop for HashX {
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fn drop(&mut self) {
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let ctx = std::mem::replace(&mut self.0, std::ptr::null_mut());
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let ctx = mem::replace(&mut self.ctx, null_mut());
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unsafe {
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ffi::hashx_free(ctx);
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}
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@ -146,7 +182,7 @@ impl EquiX {
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unsafe {
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ffi::equix_verify(
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self.0,
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challenge.as_ptr() as *const std::ffi::c_void,
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challenge.as_ptr() as *const c_void,
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challenge.len(),
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solution as *const ffi::equix_solution,
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)
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@ -159,7 +195,7 @@ impl EquiX {
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unsafe {
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ffi::equix_solve(
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self.0,
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challenge.as_ptr() as *const std::ffi::c_void,
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challenge.as_ptr() as *const c_void,
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challenge.len(),
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buffer as *mut ffi::equix_solutions_buffer,
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)
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@ -169,7 +205,7 @@ impl EquiX {
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impl Drop for EquiX {
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fn drop(&mut self) {
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let ctx = std::mem::replace(&mut self.0, std::ptr::null_mut());
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let ctx = mem::replace(&mut self.0, null_mut());
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unsafe {
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ffi::equix_free(ctx);
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}
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@ -180,6 +216,8 @@ impl Drop for EquiX {
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mod tests {
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use crate::*;
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use hex_literal::hex;
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use std::cell::RefCell;
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use std::sync::Arc;
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#[test]
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fn equix_context() {
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@ -290,4 +328,52 @@ mod tests {
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assert_eq!(ctx.exec(123456), Ok(hex!("ab3d155bf4bbb0aa")));
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assert_eq!(ctx.exec(987654321123456789), Ok(hex!("8dfef0497c323274")));
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}
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#[test]
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fn rng_callback_read() {
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// Use a Rng callback to read the sequence of pseudorandom numbers
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// without changing them, and spot check the list we get back.
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let mut ctx = HashX::new(HashXType::HASHX_TRY_COMPILE);
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let seq = Arc::new(RefCell::new(Vec::new()));
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{
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let seq = seq.clone();
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ctx.rng_callback(Some(Box::new(move |value| {
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seq.borrow_mut().push(value);
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value
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})));
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}
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assert_eq!(seq.borrow().len(), 0);
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assert_eq!(ctx.make(b"abc"), HashXResult::HASHX_OK);
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assert_eq!(ctx.exec(12345).unwrap(), hex!("c0bc95da7cc30f37"));
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assert_eq!(seq.borrow().len(), 563);
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assert_eq!(
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seq.borrow()[..4],
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[
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0xf695edd02205449d,
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0x51c1ac51cd19a7d1,
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0xadf4cb303b9814cf,
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0x79793a52d965083d
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]
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);
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}
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#[test]
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fn rng_callback_replace() {
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// Use a Rng callback to replace the random number stream.
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// We have to choose the replacement somewhat carefully since
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// many stationary replacement values will cause infinite loops.
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let mut ctx = HashX::new(HashXType::HASHX_TYPE_INTERPRETED);
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let counter = Arc::new(RefCell::new(0u32));
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{
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let counter = counter.clone();
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ctx.rng_callback(Some(Box::new(move |_value| {
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*counter.borrow_mut() += 1;
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0x0807060504030201
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})));
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}
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assert_eq!(*counter.borrow(), 0);
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assert_eq!(ctx.make(b"abc"), HashXResult::HASHX_OK);
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assert_eq!(ctx.exec(12345).unwrap(), hex!("825a9b6dd5d074af"));
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assert_eq!(*counter.borrow(), 575);
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}
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}
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