[res] Optimize few functions for dtoh() as a noop

Given that right now our device on disk endianness is exactly
the same as the in-memory one, few functions can be optimized
into noops or raw memcpy

Bug: 319137634
Test: boot + atest libandroidfw_tests
Flag: EXEMPT performance optimization
Change-Id: I2f048feea7a93fb52434b128aa2905ebf1bb46cb

3 files changed, 91 insertions, 60 deletions

diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index de9991a8be5e..a8eb062a2ece 100644
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -152,12 +152,11 @@ static void fill9patchOffsets(Res_png_9patch* patch) {
     patch->colorsOffset = patch->yDivsOffset + (patch->numYDivs * sizeof(int32_t));
 }
 
-void Res_value::copyFrom_dtoh(const Res_value& src)
-{
-    size = dtohs(src.size);
-    res0 = src.res0;
-    dataType = src.dataType;
-    data = dtohl(src.data);
+void Res_value::copyFrom_dtoh_slow(const Res_value& src) {
+  size = dtohs(src.size);
+  res0 = src.res0;
+  dataType = src.dataType;
+  data = dtohl(src.data);
 }
 
 void Res_png_9patch::deviceToFile()
@@ -2031,16 +2030,6 @@ status_t ResXMLTree::validateNode(const ResXMLTree_node* node) const
 // --------------------------------------------------------------------
 // --------------------------------------------------------------------
 
-void ResTable_config::copyFromDeviceNoSwap(const ResTable_config& o) {
-    const size_t size = dtohl(o.size);
-    if (size >= sizeof(ResTable_config)) {
-        *this = o;
-    } else {
-        memcpy(this, &o, size);
-        memset(((uint8_t*)this)+size, 0, sizeof(ResTable_config)-size);
-    }
-}
-
 /* static */ size_t unpackLanguageOrRegion(const char in[2], const char base,
         char out[4]) {
   if (in[0] & 0x80) {
@@ -2105,34 +2094,33 @@ size_t ResTable_config::unpackRegion(char region[4]) const {
     return unpackLanguageOrRegion(this->country, '0', region);
 }
 
-
-void ResTable_config::copyFromDtoH(const ResTable_config& o) {
-    copyFromDeviceNoSwap(o);
-    size = sizeof(ResTable_config);
-    mcc = dtohs(mcc);
-    mnc = dtohs(mnc);
-    density = dtohs(density);
-    screenWidth = dtohs(screenWidth);
-    screenHeight = dtohs(screenHeight);
-    sdkVersion = dtohs(sdkVersion);
-    minorVersion = dtohs(minorVersion);
-    smallestScreenWidthDp = dtohs(smallestScreenWidthDp);
-    screenWidthDp = dtohs(screenWidthDp);
-    screenHeightDp = dtohs(screenHeightDp);
-}
-
-void ResTable_config::swapHtoD() {
-    size = htodl(size);
-    mcc = htods(mcc);
-    mnc = htods(mnc);
-    density = htods(density);
-    screenWidth = htods(screenWidth);
-    screenHeight = htods(screenHeight);
-    sdkVersion = htods(sdkVersion);
-    minorVersion = htods(minorVersion);
-    smallestScreenWidthDp = htods(smallestScreenWidthDp);
-    screenWidthDp = htods(screenWidthDp);
-    screenHeightDp = htods(screenHeightDp);
+void ResTable_config::copyFromDtoH_slow(const ResTable_config& o) {
+  copyFromDeviceNoSwap(o);
+  size = sizeof(ResTable_config);
+  mcc = dtohs(mcc);
+  mnc = dtohs(mnc);
+  density = dtohs(density);
+  screenWidth = dtohs(screenWidth);
+  screenHeight = dtohs(screenHeight);
+  sdkVersion = dtohs(sdkVersion);
+  minorVersion = dtohs(minorVersion);
+  smallestScreenWidthDp = dtohs(smallestScreenWidthDp);
+  screenWidthDp = dtohs(screenWidthDp);
+  screenHeightDp = dtohs(screenHeightDp);
+}
+
+void ResTable_config::swapHtoD_slow() {
+  size = htodl(size);
+  mcc = htods(mcc);
+  mnc = htods(mnc);
+  density = htods(density);
+  screenWidth = htods(screenWidth);
+  screenHeight = htods(screenHeight);
+  sdkVersion = htods(sdkVersion);
+  minorVersion = htods(minorVersion);
+  smallestScreenWidthDp = htods(smallestScreenWidthDp);
+  screenWidthDp = htods(screenWidthDp);
+  screenHeightDp = htods(screenHeightDp);
 }
 
 /* static */ inline int compareLocales(const ResTable_config &l, const ResTable_config &r) {
@@ -2145,7 +2133,7 @@ void ResTable_config::swapHtoD() {
     // systems should happen very infrequently (if at all.)
     // The comparison code relies on memcmp low-level optimizations that make it
     // more efficient than strncmp.
-    const char emptyScript[sizeof(l.localeScript)] = {'\0', '\0', '\0', '\0'};
+    static constexpr char emptyScript[sizeof(l.localeScript)] = {'\0', '\0', '\0', '\0'};
     const char *lScript = l.localeScriptWasComputed ? emptyScript : l.localeScript;
     const char *rScript = r.localeScriptWasComputed ? emptyScript : r.localeScript;
 
diff --git a/libs/androidfw/Util.cpp b/libs/androidfw/Util.cpp
index be55fe8b4bb6..86c459fb4647 100644
--- a/libs/androidfw/Util.cpp
+++ b/libs/androidfw/Util.cpp
@@ -32,13 +32,18 @@ namespace android {
 namespace util {
 
 void ReadUtf16StringFromDevice(const uint16_t* src, size_t len, std::string* out) {
-  char buf[5];
-  while (*src && len != 0) {
-    char16_t c = static_cast<char16_t>(dtohs(*src));
-    utf16_to_utf8(&c, 1, buf, sizeof(buf));
-    out->append(buf, strlen(buf));
-    ++src;
-    --len;
+  static constexpr bool kDeviceEndiannessSame = dtohs(0x1001) == 0x1001;
+  if constexpr (kDeviceEndiannessSame) {
+    *out = Utf16ToUtf8({(const char16_t*)src, strnlen16((const char16_t*)src, len)});
+  } else {
+    char buf[5];
+    while (*src && len != 0) {
+      char16_t c = static_cast<char16_t>(dtohs(*src));
+      utf16_to_utf8(&c, 1, buf, sizeof(buf));
+      out->append(buf, strlen(buf));
+      ++src;
+      --len;
+    }
   }
 }
 
@@ -63,8 +68,10 @@ std::string Utf16ToUtf8(StringPiece16 utf16) {
   }
 
   std::string utf8;
-  utf8.resize(utf8_length);
-  utf16_to_utf8(utf16.data(), utf16.length(), &*utf8.begin(), utf8_length + 1);
+  utf8.resize_and_overwrite(utf8_length, [&utf16](char* data, size_t size) {
+    utf16_to_utf8(utf16.data(), utf16.length(), data, size + 1);
+    return size;
+  });
   return utf8;
 }
 
diff --git a/libs/androidfw/include/androidfw/ResourceTypes.h b/libs/androidfw/include/androidfw/ResourceTypes.h
index e330410ed1a0..819fe4b38c87 100644
--- a/libs/androidfw/include/androidfw/ResourceTypes.h
+++ b/libs/androidfw/include/androidfw/ResourceTypes.h
@@ -47,6 +47,8 @@
 
 namespace android {
 
+constexpr const bool kDeviceEndiannessSame = dtohs(0x1001) == 0x1001;
+
 constexpr const uint32_t kIdmapMagic = 0x504D4449u;
 constexpr const uint32_t kIdmapCurrentVersion = 0x0000000Au;
 
@@ -408,7 +410,16 @@ struct Res_value
     typedef uint32_t data_type;
     data_type data;
 
-    void copyFrom_dtoh(const Res_value& src);
+    void copyFrom_dtoh(const Res_value& src) {
+      if constexpr (kDeviceEndiannessSame) {
+        *this = src;
+      } else {
+        copyFrom_dtoh_slow(src);
+      }
+    }
+
+   private:
+    void copyFrom_dtoh_slow(const Res_value& src);
 };
 
 /**
@@ -1254,11 +1265,32 @@ struct ResTable_config
     // Varies in length from 3 to 8 chars. Zero-filled value.
     char localeNumberingSystem[8];
 
-    void copyFromDeviceNoSwap(const ResTable_config& o);
-    
-    void copyFromDtoH(const ResTable_config& o);
-    
-    void swapHtoD();
+    void copyFromDeviceNoSwap(const ResTable_config& o) {
+      const auto o_size = dtohl(o.size);
+      if (o_size >= sizeof(ResTable_config)) [[likely]] {
+        *this = o;
+      } else {
+        memcpy(this, &o, o_size);
+        memset(((uint8_t*)this) + o_size, 0, sizeof(ResTable_config) - o_size);
+      }
+      this->size = sizeof(*this);
+    }
+
+    void copyFromDtoH(const ResTable_config& o) {
+      if constexpr (kDeviceEndiannessSame) {
+        copyFromDeviceNoSwap(o);
+      } else {
+        copyFromDtoH_slow(o);
+      }
+    }
+
+    void swapHtoD() {
+      if constexpr (kDeviceEndiannessSame) {
+        ;  // noop
+      } else {
+        swapHtoD_slow();
+      }
+    }
 
     int compare(const ResTable_config& o) const;
     int compareLogical(const ResTable_config& o) const;
@@ -1384,6 +1416,10 @@ struct ResTable_config
     bool isBetterThanBeforeLocale(const ResTable_config& o, const ResTable_config* requested) const;
 
     String8 toString() const;
+
+   private:
+    void copyFromDtoH_slow(const ResTable_config& o);
+    void swapHtoD_slow();
 };
 
 /**