static void hap_write_section_header(void *buffer, size_t header_length, uint32_t section_length, unsigned int section_type)
{
/*
The first three bytes are the length of the section (not including the header) or zero
if using an eight-byte header
*/
if (header_length == 4U)
{
hap_write_3_byte_uint(buffer, (unsigned int)section_length);
}
else
{
/*
For an eight-byte header, the length is in the last four bytes
*/
hap_write_3_byte_uint(buffer, 0U);
hap_write_4_byte_uint(((uint8_t *)buffer) + 4U, section_length);
}
/*
The fourth byte stores the section type
*/
*(((uint8_t *)buffer) + 3) = section_type;
}
static unsigned int hap_encode_texture(const void *inputBuffer, unsigned long inputBufferBytes, unsigned int textureFormat,
unsigned int compressor, unsigned int chunkCount, void *outputBuffer,
unsigned long outputBufferBytes, unsigned long *outputBufferBytesUsed)
{
size_t top_section_header_length;
size_t top_section_length;
unsigned int storedCompressor;
unsigned int storedFormat;
/*
Check arguments
*/
if (inputBuffer == NULL
|| inputBufferBytes == 0
|| (textureFormat != HapTextureFormat_RGB_DXT1
&& textureFormat != HapTextureFormat_RGBA_DXT5
&& textureFormat != HapTextureFormat_YCoCg_DXT5
&& textureFormat != HapTextureFormat_A_RGTC1
)
|| (compressor != HapCompressorNone
&& compressor != HapCompressorSnappy
)
|| outputBuffer == NULL
|| outputBufferBytesUsed == NULL
)
{
return HapResult_Bad_Arguments;
}
else if (outputBufferBytes < hap_max_encoded_length(inputBufferBytes, textureFormat, compressor, chunkCount))
{
return HapResult_Buffer_Too_Small;
}
/*
To store frames of length greater than can be expressed in three bytes, we use an eight byte header (the last four bytes are the
frame size). We don't know the compressed size until we have performed compression, but we know the worst-case size
(the uncompressed size), so choose header-length based on that.
A simpler encoder could always use the eight-byte header variation.
*/
if (inputBufferBytes > kHapUInt24Max)
{
top_section_header_length = 8U;
}
else
{
top_section_header_length = 4U;
}
if (compressor == HapCompressorSnappy)
{
/*
We attempt to chunk as requested, and if resulting frame is larger than it is uncompressed then
store frame uncompressed
*/
size_t decode_instructions_length;
size_t chunk_size, compress_buffer_remaining;
uint8_t *second_stage_compressor_table;
void *chunk_size_table;
char *compressed_data;
unsigned int i;
chunkCount = hap_limited_chunk_count_for_frame(inputBufferBytes, textureFormat, chunkCount);
decode_instructions_length = hap_decode_instructions_length(chunkCount);
// Check we have space for the Decode Instructions Container
if ((inputBufferBytes + decode_instructions_length + 4) > kHapUInt24Max)
{
top_section_header_length = 8U;
}
second_stage_compressor_table = ((uint8_t *)outputBuffer) + top_section_header_length + 4 + 4;
chunk_size_table = ((uint8_t *)outputBuffer) + top_section_header_length + 4 + 4 + chunkCount + 4;
chunk_size = inputBufferBytes / chunkCount;
// write the Decode Instructions section header
hap_write_section_header(((uint8_t *)outputBuffer) + top_section_header_length, 4U, decode_instructions_length, kHapSectionDecodeInstructionsContainer);
// write the Second Stage Compressor Table section header
hap_write_section_header(((uint8_t *)outputBuffer) + top_section_header_length + 4U, 4U, chunkCount, kHapSectionChunkSecondStageCompressorTable);
// write the Chunk Size Table section header
hap_write_section_header(((uint8_t *)outputBuffer) + top_section_header_length + 4U + 4U + chunkCount, 4U, chunkCount * 4U, kHapSectionChunkSizeTable);
compressed_data = (char *)(((uint8_t *)outputBuffer) + top_section_header_length + 4 + decode_instructions_length);
compress_buffer_remaining = outputBufferBytes - top_section_header_length - 4 - decode_instructions_length;
top_section_length = 4 + decode_instructions_length;
for (i = 0; i < chunkCount; i++) {
size_t chunk_packed_length = compress_buffer_remaining;
const char *chunk_input_start = (const char *)(((uint8_t *)inputBuffer) + (chunk_size * i));
if (compressor == HapCompressorSnappy)
{
snappy_status result = snappy_compress(chunk_input_start, chunk_size, (char *)compressed_data, &chunk_packed_length);
if (result != SNAPPY_OK)
{
return HapResult_Internal_Error;
}
}
if (compressor == HapCompressorNone || chunk_packed_length >= chunk_size)
{
// store the chunk uncompressed
memcpy(compressed_data, chunk_input_start, chunk_size);
chunk_packed_length = chunk_size;
second_stage_compressor_table[i] = kHapCompressorNone;
}
else
{
// ie we used snappy and saved some space
second_stage_compressor_table[i] = kHapCompressorSnappy;
}
hap_write_4_byte_uint(((uint8_t *)chunk_size_table) + (i * 4), chunk_packed_length);
compressed_data += chunk_packed_length;
top_section_length += chunk_packed_length;
compress_buffer_remaining -= chunk_packed_length;
}
if (top_section_length < inputBufferBytes + top_section_header_length)
{
// use the complex storage because snappy compression saved space
storedCompressor = kHapCompressorComplex;
}
else
{
// Signal to store the frame uncompressed
compressor = HapCompressorNone;
}
}
if (compressor == HapCompressorNone)
{
memcpy(((uint8_t *)outputBuffer) + top_section_header_length, inputBuffer, inputBufferBytes);
top_section_length = inputBufferBytes;
storedCompressor = kHapCompressorNone;
}
storedFormat = hap_texture_format_identifier_for_format_constant(textureFormat);
hap_write_section_header(outputBuffer, top_section_header_length, top_section_length, hap_4_bit_packed_byte(storedCompressor, storedFormat));
*outputBufferBytesUsed = top_section_length + top_section_header_length;
return HapResult_No_Error;
}