[libc] [llvm] [libc] Add fixed point support to printf (PR #82707)

[Nick Desaulniers via llvm-commits]

================
@@ -0,0 +1,144 @@
+//===-- printf_fixed_conv_fuzz.cpp ----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc printf %f/e/g/a implementations.
+///
+//===----------------------------------------------------------------------===//
+#include "src/stdio/snprintf.h"
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+#include "src/__support/fixed_point/fx_bits.h"
+#include "src/__support/fixed_point/fx_rep.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "utils/MPFRWrapper/mpfr_inc.h"
+
+constexpr int MAX_SIZE = 10000;
+
+inline bool simple_streq(char *first, char *second, int length) {
+  for (int i = 0; i < length; ++i) {
+    if (first[i] != second[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+enum class TestResult {
+  Success,
+  BufferSizeFailed,
+  LengthsDiffer,
+  StringsNotEqual,
+};
+
+template <typename F>
+inline TestResult test_vals(const char *fmt, uint64_t num, int prec,
+                            int width) {
+  typename LIBC_NAMESPACE::fixed_point::FXRep<F>::StorageType raw_num = num;
+
+  long double ld_num = 0.0L;
+  long double ld_fract = 0.0L;
+
+  auto raw_num_bits = LIBC_NAMESPACE::fixed_point::FXBits<F>(raw_num);
+
+  // This needs to be a float with enough bits of precision to hold the fixed
+  // point number.
+  static_assert(sizeof(long double) > sizeof(long accum));
+
+  // build a long double that is equivalent to the fixed point number.
+  ld_num = static_cast<long double>(raw_num_bits.get_integral());
+  ld_fract = static_cast<long double>(raw_num_bits.get_fraction()) /
+             static_cast<long double>(1ll << raw_num_bits.get_exponent());
+
+  ld_num = ld_num + ld_fract;
+
+  if (raw_num_bits.get_sign()) {
+    ld_num = -ld_num;
+  }
+
+  // Call snprintf on a nullptr to get the buffer size.
+  int buffer_size = LIBC_NAMESPACE::snprintf(nullptr, 0, fmt, width, prec, num);
+
+  if (buffer_size < 0) {
+    return TestResult::BufferSizeFailed;
+  }
+
+  char *test_buff = new char[buffer_size + 1];
+  char *reference_buff = new char[buffer_size + 1];
+
+  int test_result = 0;
+  int reference_result = 0;
+
+  test_result = LIBC_NAMESPACE::snprintf(test_buff, buffer_size + 1, fmt, width,
+                                         prec, num);
+
+  // The fixed point format is defined to be %f equivalent.
+  reference_result = mpfr_snprintf(reference_buff, buffer_size + 1, "%*.*Lf",
+                                   width, prec, ld_num);
+
+  // All of these calls should return that they wrote the same amount.
+  if (test_result != reference_result || test_result != buffer_size) {
+    return TestResult::LengthsDiffer;
+  }
+
+  if (!simple_streq(test_buff, reference_buff, buffer_size)) {
+    return TestResult::StringsNotEqual;
+  }
----------------
nickdesaulniers wrote:

https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements

https://github.com/llvm/llvm-project/pull/82707