From 14ce33e2dca696145e987a6a7c0ce2f098fbb378 Mon Sep 17 00:00:00 2001
From: Alexey Ochapov <alexez@alexez.com>
Date: Fri, 25 Dec 2020 03:03:23 +0300
Subject: [PATCH] make `hex_digits` and shifts in `basic_data` constexpr

---
 include/fmt/format-inl.h | 13 ++++++-------
 include/fmt/format.h     | 24 +++++++-----------------
 2 files changed, 13 insertions(+), 24 deletions(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 1e38951e..4a527959 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -248,9 +248,6 @@ const typename basic_data<T>::digit_pair basic_data<T>::digits[] = {
     {'9', '0'}, {'9', '1'}, {'9', '2'}, {'9', '3'}, {'9', '4'}, {'9', '5'},
     {'9', '6'}, {'9', '7'}, {'9', '8'}, {'9', '9'}};
 
-template <typename T>
-const char basic_data<T>::hex_digits[] = "0123456789abcdef";
-
 #define FMT_POWERS_OF_10(factor)                                             \
   factor * 10, (factor)*100, (factor)*1000, (factor)*10000, (factor)*100000, \
       (factor)*1000000, (factor)*10000000, (factor)*100000000,               \
@@ -1071,10 +1068,12 @@ const char basic_data<T>::background_color[] = "\x1b[48;2;";
 template <typename T> const char basic_data<T>::reset_color[] = "\x1b[0m";
 template <typename T> const wchar_t basic_data<T>::wreset_color[] = L"\x1b[0m";
 template <typename T> const char basic_data<T>::signs[] = {0, '-', '+', ' '};
-template <typename T>
-const char basic_data<T>::left_padding_shifts[] = {31, 31, 0, 1, 0};
-template <typename T>
-const char basic_data<T>::right_padding_shifts[] = {0, 31, 0, 1, 0};
+
+#if __cplusplus < 201703L
+template <typename T> const char basic_data<T>::hex_digits[];
+template <typename T> const char basic_data<T>::left_padding_shifts[];
+template <typename T> const char basic_data<T>::right_padding_shifts[];
+#endif
 
 template <typename T> struct bits {
   static FMT_CONSTEXPR_DECL const int value =
diff --git a/include/fmt/format.h b/include/fmt/format.h
index ec1a7ae1..f5c380ae 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -933,14 +933,14 @@ template <typename T = void> struct FMT_EXTERN_TEMPLATE_API basic_data {
   // GCC generates slightly better code for pairs than chars.
   using digit_pair = char[2];
   static const digit_pair digits[];
-  static const char hex_digits[];
+  static constexpr const char hex_digits[] = "0123456789abcdef";
   static const char foreground_color[];
   static const char background_color[];
   static const char reset_color[5];
   static const wchar_t wreset_color[5];
   static const char signs[];
-  static const char left_padding_shifts[5];
-  static const char right_padding_shifts[5];
+  static constexpr const char left_padding_shifts[] = {31, 31, 0, 1, 0};
+  static constexpr const char right_padding_shifts[] = {0, 31, 0, 1, 0};
 
   // DEPRECATED! These are for ABI compatibility.
   static const uint32_t zero_or_powers_of_10_32[];
@@ -1144,9 +1144,7 @@ FMT_CONSTEXPR20 Char* format_uint(Char* buffer, UInt value, int num_digits,
   buffer += num_digits;
   Char* end = buffer;
   do {
-    const char* digits = upper ? "0123456789ABCDEF"
-                               : (is_constant_evaluated() ? "0123456789abcdef"
-                                                          : data::hex_digits);
+    const char* digits = upper ? "0123456789ABCDEF" : data::hex_digits;
     unsigned digit = (value & ((1 << BASE_BITS) - 1));
     *--buffer = static_cast<Char>(BASE_BITS < 4 ? static_cast<char>('0' + digit)
                                                 : digits[digit]);
@@ -1563,17 +1561,9 @@ FMT_CONSTEXPR20 OutputIt write_padded(OutputIt out,
   unsigned spec_width = to_unsigned(specs.width);
   size_t padding = spec_width > width ? spec_width - width : 0;
   size_t left_padding = 0;
-  if (is_constant_evaluated()) {
-    const char left_padding_shifts[] = {31, 31, 0, 1, 0};
-    const char right_padding_shifts[] = {0, 31, 0, 1, 0};
-    auto* shifts =
-        align == align::left ? left_padding_shifts : right_padding_shifts;
-    left_padding = padding >> shifts[specs.align];
-  } else {
-    auto* shifts = align == align::left ? data::left_padding_shifts
-                                        : data::right_padding_shifts;
-    left_padding = padding >> shifts[specs.align];
-  }
+  auto* shifts = align == align::left ? data::left_padding_shifts
+                                      : data::right_padding_shifts;
+  left_padding = padding >> shifts[specs.align];
   auto it = reserve(out, size + padding * specs.fill.size());
   it = fill(it, left_padding, specs.fill);
   it = f(it);