Kernel: Split number-parsing code into a separate file

kernel/include/utils/StringParsing.h

@@ -0,0 +1,4 @@
+#pragma once
+
+long parse_decimal(const char* str);
+long parse_octal(const char* str);

kernel/src/init/InitRD.cpp

@@ -10,6 +10,7 @@
 #include "std/errno.h"
 #include "std/stdlib.h"
 #include "std/string.h"
+#include "utils/StringParsing.h"
 
 extern BOOTBOOT bootboot;
 
@@ -54,24 +55,14 @@ uint64_t InitRD::get_file_physical_address(InitRD::File& file)
 InitRD::File InitRD::get_file(TarHeader* header)
 {
     File result;
-    result.size = 0;
+    char null_terminated_size[13];
+    memcpy(null_terminated_size, header->size, 12);
+    null_terminated_size[12] = 0;
+    result.size = parse_octal(null_terminated_size);
     memcpy(result.name, header->name, 100);
-    long multiplier =
-        1; // why they decided to store the size as an octal-encoded string instead of an integer is beyond me
-    for (int i = 10; i >= 0; i--)
-    {
-        result.size += (multiplier * (header->size[i] - 48));
-        multiplier *= 8;
-    }
     result.addr = (void*)((uint64_t)header + TAR_BLOCKSIZE);
     result.size_in_blocks = Utilities::get_blocks_from_size(TAR_BLOCKSIZE, result.size);
-    result.mode = 0;
-    multiplier = 1;
-    for (int i = 6; i >= 0; i--)
-    {
-        result.mode += (mode_t)(multiplier * (header->mode[i] - 48));
-        multiplier *= 8;
-    }
+    result.mode = (mode_t)parse_octal(header->mode);
     return result;
 }
 

kernel/src/utils/StringParsing.cpp

@@ -0,0 +1,49 @@
+#include "utils/StringParsing.h"
+
+int isdigit(int c)
+{
+    return c >= '0' && c < ':';
+}
+
+int isodigit(int c)
+{
+    return c >= '0' && c < '8';
+}
+
+int isxdigit(int c)
+{
+    return isdigit(c) || ((unsigned int)c | 32) - 'a' < 6;
+}
+
+template <typename T, typename ValidDigitChecker, typename Converter>
+static T string_to_integer_type(const char* str, int base, ValidDigitChecker checker, Converter converter)
+{
+    bool neg = false;
+    T val = 0;
+
+    switch (*str)
+    {
+    case '-':
+        neg = true;
+        str++;
+        break;
+    case '+': str++; break;
+    default: break;
+    }
+
+    while (checker(*str)) { val = (base * val) + converter(*str++); }
+
+    return (neg ? -val : val);
+}
+
+long parse_decimal(const char* str)
+{
+    return string_to_integer_type<long>(
+        str, 10, [](char c) { return isdigit(c); }, [](char c) { return c - '0'; });
+}
+
+long parse_octal(const char* str)
+{
+    return string_to_integer_type<long>(
+        str, 8, [](char c) { return isodigit(c); }, [](char c) { return c - '0'; });
+}