From 8ccceeef0dc78c022b79d76dc75adc1d2e42317b Mon Sep 17 00:00:00 2001
From: Andreas Tsouchlos <an.tsouchlos@gmail.com>
Date: Thu, 25 Nov 2021 10:16:09 +0100
Subject: [PATCH] Changed the way detail::format_args works: A preprocessing
 step yields the whole array without formatted values, values are then
 formatted in place

---
 inc/format.h                   | 225 ++++++++++++++++++---------------
 inc/parse.h                    |   2 +-
 inc/{parse_types.h => types.h} |  30 ++++-
 inc/utility.h                  |  65 +++++++++-
 4 files changed, 216 insertions(+), 106 deletions(-)
 rename inc/{parse_types.h => types.h} (82%)

diff --git a/inc/format.h b/inc/format.h
index 38b09d8..513aa89 100644
--- a/inc/format.h
+++ b/inc/format.h
@@ -15,14 +15,11 @@ constexpr void check_fmt_params() {
 }
 
 
-template <ConstString s>
-constexpr int get_output_len() {
-    constexpr auto parse_result = parse_string<s>();
-    static_assert(parse_result.is_valid, "Syntax error in format string");
-
+template <auto t_ast>
+consteval int get_ast_output_len() {
     unsigned result = 0;
 
-    for (const auto& ast_node : parse_result.value) {
+    for (const auto& ast_node : t_ast) {
         if (ast_node.is_char())
             ++result;
         else
@@ -32,112 +29,136 @@ constexpr int get_output_len() {
     return result;
 }
 
-// TODO: See if this is possible with <charconv>
-// TODO: Steal some code from fmtlib
-// TODO: In case of error, set chars to all 'f's
-template <fmt_node_t fmt_node, std::integral arg_t>
-constexpr std::array<char, fmt_node.length> format_arg(arg_t arg) {
-    check_fmt_params<fmt_node, arg_t>();
+template <ConstString s>
+constexpr int get_output_len() {
+    constexpr auto parse_result = parse_string<s>();
+    static_assert(parse_result.is_valid, "Syntax error in format string");
 
-    auto result = get_init_array<fmt_node>();
-
-    unsigned offset = 0;
-
-    if (arg < 0) {
-        result[0] = '-';
-        arg = -arg;
-        ++offset;
-    }
-
-    for (int i = result.size() - 1; (i >= static_cast<int>(offset)) && (arg > 0); --i) {
-        result[i] = arg % 10 + 48;
-        arg       = arg / 10;
-    }
-
-    return result;
+    return get_ast_output_len<parse_result.value>();
 }
 
-// TODO: See if this is possible with <charconv>
-// TODO: Steal some code from fmtlib
-// TODO: In case of error, set chars to all 'f's
-template <fmt_node_t fmt_node, std::floating_point arg_t>
-constexpr std::array<char, fmt_node.length> format_arg(arg_t arg) {
-    check_fmt_params<fmt_node, arg_t>();
+//// TODO: See if this is possible with <charconv>
+//// TODO: Steal some code from fmtlib
+//// TODO: In case of error, set chars to all 'f's
+// template <fmt_node_t fmt_node, std::integral arg_t>
+// constexpr std::array<char, fmt_node.length> format_arg(arg_t arg) {
+//     check_fmt_params<fmt_node, arg_t>();
+//
+//     auto result = get_init_array<fmt_node>();
+//
+//     unsigned offset = 0;
+//
+//     if (arg < 0) {
+//         result[0] = '-';
+//         arg       = -arg;
+//         ++offset;
+//     }
+//
+//     for (int i = result.size() - 1;
+//          (i >= static_cast<int>(offset)) && (arg > 0); --i) {
+//         result[i] = arg % 10 + 48;
+//         arg       = arg / 10;
+//     }
+//
+//     return result;
+// }
+//
+//// TODO: See if this is possible with <charconv>
+//// TODO: Steal some code from fmtlib
+//// TODO: In case of error, set chars to all 'f's
+// template <fmt_node_t fmt_node, std::floating_point arg_t>
+// constexpr std::array<char, fmt_node.length> format_arg(arg_t arg) {
+//     check_fmt_params<fmt_node, arg_t>();
+//
+//     constexpr unsigned point_index = fmt_node.length - fmt_node.precision -
+//     1; constexpr unsigned multiplier  = const_pow(10, fmt_node.precision);
+//
+//     auto result         = get_init_array<fmt_node>();
+//     result[point_index] = '.';
+//
+//
+//     arg = arg * multiplier;
+//
+//     for (int i = result.size() - 1;
+//          (i > static_cast<int>(point_index)) && (arg >= 1); --i) {
+//
+//         result[i] = static_cast<int>(arg) % 10 + 48;
+//         arg       = arg / 10;
+//     }
+//
+//     for (int i = point_index - 1; (i >= 0) && (arg >= 1); --i) {
+//         result[i] = static_cast<int>(arg) % 10 + 48;
+//         arg       = arg / 10;
+//     }
+//
+//     return result;
+// }
+//
+//// TODO: Steal some code from fmtlib
+//// TODO: In case of error, set chars to all 'f's
+// template <fmt_node_t fmt_node>
+// constexpr std::array<char, fmt_node.length> format_arg(const char* arg) {
+//     check_fmt_params<fmt_node, const char*>();
+//
+//     std::array<char, fmt_node.length> result;
+//
+//     for (auto& c : result) {
+//         if (*arg != '\0')
+//             c = *(arg++);
+//         else
+//             c = ' ';
+//     }
+//
+//     return result;
+// }
+//
+//
+// template <auto t_ast, unsigned t_ast_i = 0, unsigned t_result_i = 0,
+//           typename char_array_t>
+// constexpr char_array_t format_args(char_array_t result) {
+//     return result;
+// }
 
-    constexpr unsigned point_index = fmt_node.length - fmt_node.precision - 1;
-    constexpr unsigned multiplier  = const_pow(10, fmt_node.precision);
+template <auto ast>
+consteval std::array<char, get_ast_output_len<ast>()> get_preproc_string() {
+    auto result = get_zero_array<get_ast_output_len<ast>()>();
 
-    auto result         = get_init_array<fmt_node>();
-    result[point_index] = '.';
+    int i = 0;
 
-
-    arg = arg * multiplier;
-
-    for (int i = result.size() - 1;
-         (i > static_cast<int>(point_index)) && (arg >= 1); --i) {
-
-        result[i] = static_cast<int>(arg) % 10 + 48;
-        arg       = arg / 10;
-    }
-
-    for (int i = point_index - 1; (i >= 0) && (arg >= 1); --i) {
-        result[i] = static_cast<int>(arg) % 10 + 48;
-        arg       = arg / 10;
-    }
-
-    return result;
-}
-
-// TODO: Steal some code from fmtlib
-// TODO: In case of error, set chars to all 'f's
-template <fmt_node_t fmt_node>
-constexpr std::array<char, fmt_node.length> format_arg(const char* arg) {
-    check_fmt_params<fmt_node, const char*>();
-
-    std::array<char, fmt_node.length> result;
-
-    for (auto& c : result) {
-        if (*arg != '\0')
-            c = *(arg++);
+    for (const auto& ast_node : ast) {
+        if (ast_node.is_char())
+            result[i++] = ast_node.get_char();
         else
-            c = ' ';
+            i += ast_node.get_node().length;
     }
 
     return result;
 }
 
 
-template <auto t_ast, unsigned t_ast_i = 0, unsigned t_result_i = 0,
-          typename char_array_t>
-constexpr char_array_t format_args(char_array_t result) {
-    return result;
+template <std::integral arg_t>
+constexpr void format_arg(char* dest, fmt_data_t fmt_data, arg_t arg) {
+    *(dest + fmt_data.position) = 'i';
+//    dest = dest + fmt_data.position;
+//    format_int(dest, fmt_data.length, arg);
+};
+template <std::floating_point arg_t>
+constexpr void format_arg(char* dest, fmt_data_t fmt_data, arg_t) {
+    *(dest + fmt_data.position) = 'f';
+};
+constexpr void format_arg(char* dest, fmt_data_t fmt_data, const char*) {
+    *(dest + fmt_data.position) = 'c';
+};
+
+
+template <auto ast>
+constexpr void format_args(char*) {
 }
 
-template <auto t_ast, unsigned t_ast_i = 0, unsigned t_result_i = 0,
-          typename char_array_t, typename first_arg_t, typename... other_args_t>
-constexpr char_array_t format_args(char_array_t result, first_arg_t first_arg,
-                                   other_args_t... other_args) {
-    if constexpr (t_ast_i >= t_ast.size()) {
-        return result;
-    } else {
-        constexpr auto ast_node = t_ast[t_ast_i];
-
-        if (ast_node.is_char()) {
-            result[t_result_i] = ast_node.get_char();
-            return format_args<t_ast, t_ast_i + 1, t_result_i + 1>(
-                result, first_arg, other_args...);
-        } else {
-            constexpr auto fmt_node      = ast_node.get_node();
-            const auto     formatted_arg = format_arg<fmt_node>(first_arg);
-
-            std::copy(formatted_arg.begin(), formatted_arg.end(),
-                      result.begin() + t_result_i);
-
-            return format_args<t_ast, t_ast_i + 1,
-                               t_result_i + fmt_node.length>(result,
-                                                             other_args...);
-        }
-    }
+template <auto fmt_data_array, typename first_arg_t, typename... args_t>
+constexpr void format_args(char* dest, first_arg_t first_arg, args_t... args) {
+    format_arg(dest, fmt_data_array[0], first_arg);
+    format_args<drop_first(fmt_data_array)>(dest, args...);
 }
 
 
@@ -146,12 +167,14 @@ constexpr char_array_t format_args(char_array_t result, first_arg_t first_arg,
 
 template <detail::ConstString s, typename... args_t>
 constexpr std::array<char, detail::get_output_len<s>()> format(args_t... args) {
-    constexpr auto parse_result = detail::parse_string<s>();
-    static_assert(parse_result.is_valid, "Syntax error in format string");
+    constexpr auto ast      = detail::parse_string<s>().value;
+    constexpr auto fmt_data = detail::get_fmt_data<ast>();
 
-    std::array<char, detail::get_output_len<s>()> result = {};
+    auto result = detail::get_preproc_string<ast>();
 
-    return detail::format_args<parse_result.value>(result, args...);
+    detail::format_args<fmt_data>(result.begin(), args...);
+
+    return result;
 }
 
 
diff --git a/inc/parse.h b/inc/parse.h
index 03fcc8b..a9a1260 100644
--- a/inc/parse.h
+++ b/inc/parse.h
@@ -3,7 +3,7 @@
 
 
 #include "ConstString.h"
-#include "parse_types.h"
+#include "types.h"
 
 
 // clang-format off
diff --git a/inc/parse_types.h b/inc/types.h
similarity index 82%
rename from inc/parse_types.h
rename to inc/types.h
index 46b551f..d0fcd81 100644
--- a/inc/parse_types.h
+++ b/inc/types.h
@@ -1,5 +1,5 @@
-#ifndef LOGGER_PARSE_TYPES_H
-#define LOGGER_PARSE_TYPES_H
+#ifndef LOGGER_TYPES_H
+#define LOGGER_TYPES_H
 
 
 #include <array>
@@ -8,6 +8,13 @@
 namespace detail {
 
 
+/*
+ *
+ * Types used mainly in parsing
+ *
+ */
+
+
 enum class FormatType { s, c, b, B, d, o, x, X, a, A, e, E, f, F, g, G, p };
 
 
@@ -81,7 +88,24 @@ template <std::size_t N>
 using string_result_t = std::array<ast_node_t, N>;
 
 
+/*
+ *
+ * Types used mainly in formatting
+ *
+ */
+
+
+struct fmt_data_t {
+    bool        has_zero_padding = 0;
+    std::size_t length           = 0;
+    std::size_t precision        = 0;
+    FormatType  type;
+
+    std::size_t position = 0;
+};
+
+
 } // namespace detail
 
 
-#endif // LOGGER_PARSE_TYPES_H
+#endif // LOGGER_TYPES_H
diff --git a/inc/utility.h b/inc/utility.h
index 26f41a7..284a3e4 100644
--- a/inc/utility.h
+++ b/inc/utility.h
@@ -2,7 +2,7 @@
 #define LOGGER_UTILITY_H
 
 
-#include "parse_types.h"
+#include "types.h"
 
 
 namespace detail {
@@ -16,6 +16,16 @@ constexpr std::size_t const_pow(std::size_t base, std::size_t pow) {
 }
 
 
+template <std::size_t t_n>
+constexpr std::array<char, t_n> get_zero_array() {
+    std::array<char, t_n> result;
+
+    for (auto& c : result)
+        c = '0';
+
+    return result;
+}
+
 template <fmt_node_t fmt_node>
 constexpr std::array<char, fmt_node.length> get_init_array() {
     std::array<char, fmt_node.length> result;
@@ -32,6 +42,59 @@ constexpr std::array<char, fmt_node.length> get_init_array() {
 }
 
 
+template <auto ast>
+consteval std::size_t count_ast_format_nodes() {
+    std::size_t result = 0;
+
+    for (const auto& node : ast)
+        if (!node.is_char()) ++result;
+
+    return result;
+}
+
+
+template <auto ast>
+consteval std::array<fmt_data_t, count_ast_format_nodes<ast>()> get_fmt_data() {
+    std::array<fmt_data_t, count_ast_format_nodes<ast>()> result = {};
+
+    std::size_t position = 0;
+    std::size_t i        = 0;
+
+    for (const auto& node : ast) {
+        if (!node.is_char()) {
+            const auto fmt_node = node.get_node();
+
+            result[i].has_zero_padding = fmt_node.has_zero_padding;
+            result[i].length           = fmt_node.length;
+            result[i].precision        = fmt_node.precision;
+            result[i].type             = fmt_node.type;
+            result[i].position         = position;
+
+            ++i;
+            position += fmt_node.length;
+        } else {
+            ++position;
+        }
+    }
+
+    return result;
+}
+
+
+template <typename elem_t, std::size_t t_n>
+consteval std::array<elem_t, t_n - 1>
+drop_first(std::array<elem_t, t_n> array) {
+    static_assert(t_n > 0,
+                  "Can't drop first element of array with no elements");
+
+    std::array<elem_t, t_n - 1> result;
+
+    std::copy(array.begin() + 1, array.end(), result.begin());
+
+    return result;
+}
+
+
 } // namespace detail