os: implement ExpandUnsignedValueToAscii

Nintendo does this as of latest firmware.

It's desirable because it removes the only usage of util::SNPrintf() from os library,
which means programs which don't otherwise use SNPrintf do not need to link it into .text.

This saves ~0xD40 of .text as of time-of-commit when successfully unlinking, and e.g.
reduces our sm (and other modules) memory size by a page.

libraries/libstratosphere/source/os/impl/os_thread_manager.cpp

@@ -19,6 +19,7 @@
 #include "os_waitable_holder_base.hpp"
 #include "os_waitable_holder_impl.hpp"
 #include "os_waitable_object_list.hpp"
+#include "os_utility.hpp"
 
 namespace ams::os::impl {
 
@@ -223,7 +224,8 @@ namespace ams::os::impl {
             constexpr size_t ThreadNamePrefixSize = sizeof(ThreadNamePrefix) - 1;
             const u64 func = reinterpret_cast<u64>(thread->function);
             static_assert(ThreadNamePrefixSize + sizeof(func) * 2 + 1 <= sizeof(thread->name_buffer));
-            util::SNPrintf(thread->name_buffer, sizeof(thread->name_buffer), "%s%016lX", ThreadNamePrefix, func);
+            std::memcpy(thread->name_buffer, ThreadNamePrefix, ThreadNamePrefixSize);
+            os::impl::ExpandUnsignedValueToAscii(thread->name_buffer + ThreadNamePrefixSize, func);
         }
 
         thread->name_pointer = thread->name_buffer;

libraries/libstratosphere/source/os/impl/os_utility.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "os_utility.hpp"
+
+namespace ams::os::impl {
+
+    void ExpandUnsignedValueToAscii(char *dst, u64 value) {
+        /* Determine size needed. */
+        constexpr size_t SizeNeeded = (BITSIZEOF(value) / 4) * sizeof(char);
+
+        /* Write null-terminator. */
+        dst[SizeNeeded] = '\x00';
+
+        /* Write characters. */
+        for (size_t i = 0; i < SizeNeeded; ++i) {
+            /* Determine current character. */
+            const auto nybble = (value & 0xF);
+            const char cur_c  = (nybble < 10) ? ('0' + nybble) : ('A' + nybble - 10);
+
+            /* Write current character. */
+            dst[SizeNeeded - 1 - i] = cur_c;
+
+            /* Shift to next nybble. */
+            value >>= 4;
+        }
+    }
+
+}

libraries/libstratosphere/source/os/impl/os_utility.hpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include "os_waitable_holder_base.hpp"
+#include "os_waitable_manager_impl.hpp"
+
+namespace ams::os::impl {
+
+    void ExpandUnsignedValueToAscii(char *dst, u64 value);
+
+}