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[api] Read fixed32 fields with byte loads and test the varint wire type first

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ESP-IDF passes -fno-builtin-memcpy, so the four byte memcpy in the decode loop was an
out of line call on every fixed32 field; host compilers fold the byte loads back into one
load. Checking the varint wire type first keeps the common path to one taken branch on
xtensa.
This commit is contained in:
J. Nick Koston
2026-09-07 15:57:13 +02:00
parent 2bc20d8721
commit cbdcfe640c
1 changed files with 37 additions and 43 deletions
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esphome/components/api/proto.cpp
+37 -43
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@@ -218,7 +218,7 @@ void ProtoDecodableMessage::decode(const uint8_t *buffer, size_t length) {
auto read_varint = [&](proto_varint_value_t &value) ESPHOME_ALWAYS_INLINE {
if (ptr == end)
return false;
if ((*ptr & 0x80) == 0) [[likely]] {
if (*ptr < 0x80) [[likely]] {
value = *ptr++;
return true;
}
@@ -243,49 +243,43 @@ void ProtoDecodableMessage::decode(const uint8_t *buffer, size_t length) {
const uint8_t *data = ptr;
proto_varint_value_t scalar;
switch (field_type) {
case WIRE_TYPE_VARINT: { // VarInt
if (!read_varint(scalar)) {
ESP_LOGV(TAG, "Invalid VarInt at offset %ld", (long) (ptr - buffer));
return;
}
break;
}
case WIRE_TYPE_LENGTH_DELIMITED: { // Length-delimited
proto_varint_value_t length_value;
if (!read_varint(length_value)) {
ESP_LOGV(TAG, "Invalid Length Delimited at offset %ld", (long) (ptr - buffer));
return;
}
uint32_t field_length = static_cast<uint32_t>(length_value);
if (field_length > static_cast<size_t>(end - ptr)) {
ESP_LOGV(TAG, "Out-of-bounds Length Delimited at offset %ld", (long) (ptr - buffer));
return;
}
data = ptr;
scalar = field_length;
ptr += field_length;
break;
}
case WIRE_TYPE_FIXED32: { // 32-bit
if (end - ptr < 4) {
ESP_LOGV(TAG, "Out-of-bounds Fixed32-bit at offset %ld", (long) (ptr - buffer));
return;
}
uint32_t val;
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
// Protobuf fixed32 is little-endian — direct load on LE platforms
memcpy(&val, ptr, 4);
#else
val = encode_uint32(ptr[3], ptr[2], ptr[1], ptr[0]);
#endif
scalar = val;
ptr += 4;
break;
}
default:
ESP_LOGV(TAG, "Invalid field type %" PRIu32 " at offset %ld", field_type, (long) (ptr - buffer));
if (field_type == WIRE_TYPE_VARINT) [[likely]] {
if (!read_varint(scalar)) {
ESP_LOGV(TAG, "Invalid VarInt at offset %ld", (long) (ptr - buffer));
return;
}
} else {
switch (field_type) {
case WIRE_TYPE_LENGTH_DELIMITED: {
proto_varint_value_t length_value;
if (!read_varint(length_value)) {
ESP_LOGV(TAG, "Invalid Length Delimited at offset %ld", (long) (ptr - buffer));
return;
}
uint32_t field_length = static_cast<uint32_t>(length_value);
if (field_length > static_cast<size_t>(end - ptr)) {
ESP_LOGV(TAG, "Out-of-bounds Length Delimited at offset %ld", (long) (ptr - buffer));
return;
}
data = ptr;
scalar = field_length;
ptr += field_length;
break;
}
case WIRE_TYPE_FIXED32: {
if (end - ptr < 4) {
ESP_LOGV(TAG, "Out-of-bounds Fixed32-bit at offset %ld", (long) (ptr - buffer));
return;
}
// Byte loads instead of memcpy: ESP-IDF passes -fno-builtin-memcpy, which made this a call
scalar = encode_uint32(ptr[3], ptr[2], ptr[1], ptr[0]);
ptr += 4;
break;
}
default:
ESP_LOGV(TAG, "Invalid field type %" PRIu32 " at offset %ld", field_type, (long) (ptr - buffer));
return;
}
}
if (!this->decode_field(tag, data, scalar)) {
ESP_LOGV(TAG, "Cannot decode field %" PRIu32 " with wire type %" PRIu32 "!", tag >> 3, field_type);