From c2daa8a614b2d412d12ae8d289b0ab7019d6989a Mon Sep 17 00:00:00 2001
From: IRainman <a.rainman@gmail.com>
Date: Sun, 9 Mar 2025 03:41:27 +0300
Subject: [PATCH] Added FASTFLOAT_ASSUME for support attribute [[assume]] is
 declared in P1774

---
 include/fast_float/ascii_number.h             | 2 +-
 include/fast_float/constexpr_feature_detect.h | 9 +++++++++
 include/fast_float/float_common.h             | 2 +-
 include/fast_float/parse_number.h             | 6 +++---
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/fast_float/ascii_number.h b/include/fast_float/ascii_number.h
index c5b93f4..ca47afd 100644
--- a/include/fast_float/ascii_number.h
+++ b/include/fast_float/ascii_number.h
@@ -291,7 +291,7 @@ parse_number_string(UC const *p, UC const *pend,
   parsed_number_string_t<UC> answer;
   answer.valid = false;
   answer.too_many_digits = false;
-  [[assume(p < pend)]]; // assume p < pend, so dereference without checks;
+  FASTFLOAT_ASSUME(p < pend); // assume p < pend, so dereference without checks;
 #ifndef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
   answer.negative = (*p == UC('-'));
   // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
diff --git a/include/fast_float/constexpr_feature_detect.h b/include/fast_float/constexpr_feature_detect.h
index 26752ee..b1d1a8a 100644
--- a/include/fast_float/constexpr_feature_detect.h
+++ b/include/fast_float/constexpr_feature_detect.h
@@ -46,4 +46,13 @@
 #define FASTFLOAT_DETAIL_MUST_DEFINE_CONSTEXPR_VARIABLE 1
 #endif
 
+// For support attribute [[assume]] is declared in P1774
+#if defined(__clang__)
+#define FASTFLOAT_ASSUME(expr) __builtin_assume(expr)
+#elif defined(__GNUC__) && !defined(__ICC)
+#define ASSUME(expr) __attribute__((expr)))
+#elif defined(_MSC_VER) || defined(__ICC)
+#define FASTFLOAT_ASSUME(expr) __assume(expr)
+#endif
+
 #endif // FASTFLOAT_CONSTEXPR_FEATURE_DETECT_H
diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 7f2d002..28d8671 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -342,7 +342,7 @@ leading_zeroes_generic(uint64_t input_num, int last_bit = 0) {
 fastfloat_really_inline FASTFLOAT_CONSTEXPR20 int
 leading_zeroes(uint64_t input_num) noexcept {
   assert(input_num > 0);
-  [[assume(input_num > 0)]];
+  FASTFLOAT_ASSUME(input_num > 0);
   if (cpp20_and_in_constexpr()) {
     return leading_zeroes_generic(input_num);
   }
diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index 0798603..80eb364 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -27,7 +27,7 @@ from_chars_result_t<UC>
   from_chars_result_t<UC> answer{};
   answer.ptr = first;
   answer.ec = std::errc(); // be optimistic
-  [[assume(first < last)]]; // so dereference without checks
+  FASTFLOAT_ASSUME(first < last); // so dereference without checks
 
   bool const minusSign = (*first == UC('-'));
   // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
@@ -321,7 +321,7 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
   }
 #else
   // We are in parser code with external loop that checks bounds.
-  [[assume((first < last))]];
+  FASTFLOAT_ASSUME(first < last);
 #endif
   parsed_number_string_t<UC> const pns =
       parse_number_string<UC>(first, last, options);
@@ -374,7 +374,7 @@ from_chars_int_advanced(UC const *first, UC const *last, T &value,
   }
 #else
   // We are in parser code with external loop that checks bounds.
-  [[assume((first < last))]];
+  FASTFLOAT_ASSUME(first < last);
 #endif
   if (
 #ifndef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN