Merge pull request #383 from redis-performance/pr/parallel-exhaustive

Parallelize the exhaustive float32 sweeps across hardware threads (~75-88x)

tests/CMakeLists.txt

@@ -4,6 +4,10 @@ cmake_minimum_required(VERSION 3.11 FATAL_ERROR)
 
 include(FetchContent)
 
+# Some tests (the exhaustive sweeps) parallelize across std::thread.
+set(THREADS_PREFER_PTHREAD_FLAG ON)
+find_package(Threads REQUIRED)
+
 option(SYSTEM_DOCTEST "Use system copy of doctest" OFF)
 option(FASTFLOAT_SUPPLEMENTAL_TESTS "Run supplemental tests" ON)
 
@@ -49,6 +53,7 @@ function(fast_float_add_cpp_test TEST_NAME)
       target_compile_options(${TEST_NAME} PUBLIC -Wsign-compare -Wshadow -Wwrite-strings -Wpointer-arith -Winit-self -Wconversion -Wsign-conversion)
     endif()
     target_link_libraries(${TEST_NAME} PUBLIC fast_float supplemental-data)
+    target_link_libraries(${TEST_NAME} PUBLIC Threads::Threads)
     if (NOT SYSTEM_DOCTEST)
       target_link_libraries(${TEST_NAME} PUBLIC doctest)
     else ()

tests/exhaustive32.cpp

@@ -8,6 +8,8 @@
 #include <iostream>
 #include <limits>
 #include <system_error>
+#include <thread>
+#include <vector>
 
 template <typename T> char *to_string(T d, char *buffer) {
   auto written = std::snprintf(buffer, 64, "%.*e",
@@ -15,18 +17,12 @@ template <typename T> char *to_string(T d, char *buffer) {
   return buffer + written;
 }
 
-void allvalues() {
+// Checks a single 32-bit word (interpreted as a float); aborts on a mismatch.
+void check_word(uint32_t word) {
   char buffer[64];
-  for (uint64_t w = 0; w <= 0xFFFFFFFF; w++) {
   float v;
-    if ((w % 1048576) == 0) {
-      std::cout << ".";
-      std::cout.flush();
-    }
-    uint32_t word = uint32_t(w);
   memcpy(&v, &word, sizeof(v));
 
-    {
   char const *string_end = to_string(v, buffer);
   float result_value;
   auto result = fast_float::from_chars(buffer, string_end, result_value);
@@ -34,8 +30,7 @@ void allvalues() {
   // if the value is either too small (too close to zero) or too large
   // (effectively infinity). So std::errc::result_out_of_range is normal for
   // well-formed input strings.
-      if (result.ec != std::errc() &&
-          result.ec != std::errc::result_out_of_range) {
+  if (result.ec != std::errc() && result.ec != std::errc::result_out_of_range) {
     std::cerr << "parsing error ? " << buffer << std::endl;
     abort();
   }
@@ -56,6 +51,25 @@ void allvalues() {
     abort();
   }
 }
+
+// Sweeps the whole 2^32 float space, split across hardware threads (the values
+// are independent); check_word() aborts on the first mismatch.
+void allvalues() {
+  unsigned int nthreads = std::thread::hardware_concurrency();
+  if (nthreads == 0) {
+    nthreads = 1;
+  }
+  std::vector<std::thread> workers;
+  workers.reserve(nthreads);
+  for (unsigned int t = 0; t < nthreads; t++) {
+    workers.emplace_back([t, nthreads]() {
+      for (uint64_t w = t; w <= 0xFFFFFFFF; w += nthreads) {
+        check_word(uint32_t(w));
+      }
+    });
+  }
+  for (std::thread &worker : workers) {
+    worker.join();
   }
   std::cout << std::endl;
 }

tests/exhaustive32_64.cpp

@@ -1,6 +1,7 @@
 
 #include "fast_float/fast_float.h"
 
+#include <atomic>
 #include <cassert>
 #include <cmath>
 #include <cstdio>
@@ -9,6 +10,8 @@
 #include <limits>
 #include <string>
 #include <system_error>
+#include <thread>
+#include <vector>
 
 template <typename T> char *to_string(T d, char *buffer) {
   auto written = std::snprintf(buffer, 64, "%.*e",
@@ -45,25 +48,38 @@ bool basic_test_64bit(std::string vals, double val) {
   return true;
 }
 
+// Sweeps the whole 2^32 float space (widened to double), split across hardware
+// threads (the values are independent); stops at the first mismatch.
 void all_32bit_values() {
-  char buffer[64];
-  for (uint64_t w = 0; w <= 0xFFFFFFFF; w++) {
-    float v32;
-    if ((w % 1048576) == 0) {
-      std::cout << ".";
-      std::cout.flush();
+  unsigned int nthreads = std::thread::hardware_concurrency();
+  if (nthreads == 0) {
+    nthreads = 1;
   }
+  std::atomic<bool> ok{true};
+  std::vector<std::thread> workers;
+  workers.reserve(nthreads);
+  for (unsigned int t = 0; t < nthreads; t++) {
+    workers.emplace_back([t, nthreads, &ok]() {
+      char buffer[64];
+      for (uint64_t w = t;
+           w <= 0xFFFFFFFF && ok.load(std::memory_order_relaxed);
+           w += nthreads) {
+        float v32;
         uint32_t word = uint32_t(w);
         memcpy(&v32, &word, sizeof(v32));
         double v = v32;
 
-    {
         char const *string_end = to_string(v, buffer);
         std::string s(buffer, size_t(string_end - buffer));
         if (!basic_test_64bit(s, v)) {
+          ok.store(false, std::memory_order_relaxed);
           return;
         }
       }
+    });
+  }
+  for (std::thread &worker : workers) {
+    worker.join();
   }
   std::cout << std::endl;
 }

tests/exhaustive32_midpoint.cpp

@@ -1,5 +1,6 @@
 #include "fast_float/fast_float.h"
 
+#include <atomic>
 #include <cassert>
 #include <cmath>
 #include <cstdio>
@@ -7,6 +8,8 @@
 #include <iostream>
 #include <limits>
 #include <stdexcept>
+#include <thread>
+#include <vector>
 
 #if defined(__CYGWIN__) || defined(__MINGW32__) || defined(__MINGW64__)
 // Anything at all that is related to cygwin, msys and so forth will
@@ -74,23 +77,21 @@ void strtof_from_string(char const *st, float &d) {
   }
 }
 
-bool allvalues() {
+// Checks a single 32-bit word (interpreted as a float). Returns true if the
+// parser agrees with the reference, false (after logging) on a mismatch.
+bool check_word(uint32_t word) {
   char buffer[64];
-  for (uint64_t w = 0; w <= 0xFFFFFFFF; w++) {
   float v;
-    if ((w % 1048576) == 0) {
-      std::cout << ".";
-      std::cout.flush();
-    }
-    uint32_t word = uint32_t(w);
   memcpy(&v, &word, sizeof(v));
-    if (std::isfinite(v)) {
+  if (!std::isfinite(v)) {
+    return true;
+  }
   float nextf = std::nextafterf(v, INFINITY);
   if (copysign(1, v) != copysign(1, nextf)) {
-        continue;
+    return true;
   }
   if (!std::isfinite(nextf)) {
-        continue;
+    return true;
   }
   double v1{v};
   assert(float(v1) == v);
@@ -109,8 +110,7 @@ bool allvalues() {
   // if the value is either too small (too close to zero) or too large
   // (effectively infinity). So std::errc::result_out_of_range is normal for
   // well-formed input strings.
-      if (result.ec != std::errc() &&
-          result.ec != std::errc::result_out_of_range) {
+  if (result.ec != std::errc() && result.ec != std::errc::result_out_of_range) {
     std::cerr << "parsing error ? " << buffer << std::endl;
     return false;
   }
@@ -142,18 +142,42 @@ bool allvalues() {
     std::cerr << "expected_midv " << std::hexfloat << expected_midv
               << std::endl;
     std::cout << "started with " << std::hexfloat << midv << std::endl;
-        std::cout << "round down to " << std::hexfloat << str_answer
-                  << std::endl;
+    std::cout << "round down to " << std::hexfloat << str_answer << std::endl;
     std::cout << "got back " << std::hexfloat << result_value << std::endl;
     std::cout << std::dec;
     return false;
   }
-    }
-  }
-  std::cout << std::endl;
   return true;
 }
 
+// Sweeps the whole 2^32 float space, split across hardware threads (the values
+// are independent). Returns false as soon as any word mismatches.
+bool allvalues() {
+  unsigned int nthreads = std::thread::hardware_concurrency();
+  if (nthreads == 0) {
+    nthreads = 1;
+  }
+  std::atomic<bool> ok{true};
+  std::vector<std::thread> workers;
+  workers.reserve(nthreads);
+  for (unsigned int t = 0; t < nthreads; t++) {
+    workers.emplace_back([t, nthreads, &ok]() {
+      for (uint64_t w = t;
+           w <= 0xFFFFFFFF && ok.load(std::memory_order_relaxed);
+           w += nthreads) {
+        if (!check_word(uint32_t(w))) {
+          ok.store(false, std::memory_order_relaxed);
+          return;
+        }
+      }
+    });
+  }
+  for (std::thread &worker : workers) {
+    worker.join();
+  }
+  return ok.load();
+}
+
 inline void Assert(bool Assertion) {
 #if defined(__CYGWIN__) || defined(__MINGW32__) || defined(__MINGW64__) ||     \
     defined(sun) || defined(__sun)