From 67005a80be5ff3753bc943f0328bf672d738d456 Mon Sep 17 00:00:00 2001
From: Bananymous <bananymousosq@gmail.com>
Date: Wed, 10 May 2023 15:41:11 +0300
Subject: [PATCH] LibC: add working f modifier to printf

This is implementation will write out of bounds if the conversion
takes more than 1024 characters (either super large number or very
big percision).

Also we dont handle NaN and infinity cases
---
 libc/printf_impl.cpp | 58 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 5 deletions(-)

diff --git a/libc/printf_impl.cpp b/libc/printf_impl.cpp
index 4e92fcafc..98377ad61 100644
--- a/libc/printf_impl.cpp
+++ b/libc/printf_impl.cpp
@@ -1,3 +1,4 @@
+#include <BAN/Traits.h>
 #include <ctype.h>
 #include <errno.h>
 #include <stdio.h>
@@ -22,7 +23,7 @@ struct format_options_t
 	int percision { -1 };
 };
 
-template<typename T>
+template<BAN::integral T>
 static void integer_to_string(char* buffer, T value, int base, bool upper, const format_options_t options)
 {
 	int width = 1;
@@ -94,7 +95,7 @@ static void integer_to_string(char* buffer, T value, int base, bool upper, const
 	buffer[offset++] = '\0';
 }
 
-template<typename T>
+template<BAN::floating_point T>
 static void floating_point_to_exponent_string(char* buffer, T value, bool upper, const format_options_t options)
 {
 	int percision = 6;
@@ -104,14 +105,59 @@ static void floating_point_to_exponent_string(char* buffer, T value, bool upper,
 	strcpy(buffer, "??e??");
 }
 
-template<typename T>
+template<BAN::floating_point T>
 static void floating_point_to_string(char* buffer, T value, bool upper, const format_options_t options)
 {
 	int percision = 6;
 	if (options.percision != -1)
 		percision = options.percision;
 
-	strcpy(buffer, "??.??");
+	int offset = 0;
+
+	if (value < 0)
+	{
+		buffer[offset++] = '-';
+		value = -value;
+	}
+	else if (options.show_plus_sign)
+		buffer[offset++] = '+';
+	else if (options.show_plus_sign_as_space)
+		buffer[offset++] = ' ';
+
+	int exponent = 1;
+	while (value > exponent * 10)
+		exponent *= 10;
+
+	T fractional = value;
+	while (exponent >= 1)
+	{
+		int scale = 0;
+		for (; scale < 10; scale++)
+			if (fractional < T(exponent * (scale + 1)))
+				break;
+		buffer[offset++] = '0' + scale;
+		fractional -= T(exponent * scale);
+		exponent /= 10;
+	}
+
+	if (!options.alternate_form && percision <= 0)
+	{
+		buffer[offset++] = '\0';
+		return;
+	}
+	
+	buffer[offset++] = '.';
+	for (int i = 0; i < percision; i++)
+	{
+		fractional *= T(10.0);
+		if (i == percision - 1)
+			fractional += T(0.5);
+		int digit = fractional;
+		buffer[offset++] = '0' + digit;
+		fractional -= T(digit);
+	}
+
+	buffer[offset++] = '\0';
 }
 
 extern "C" int printf_impl(const char* format, va_list arguments, int (*putc_fun)(int, void*), void* data)
@@ -179,12 +225,14 @@ extern "C" int printf_impl(const char* format, va_list arguments, int (*putc_fun
 				{
 					percision = va_arg(arguments, int);
 				}
+				if (percision < 0)
+					percision = -1;
 				options.percision = percision;
 			}
 		
 			// TODO: Lenght modifier
 
-			static char conversion[100];
+			static char conversion[1024];
 
 			const char* string = nullptr;
 			switch (*format)