pw_bytes#

pw_bytes is a collection of utilities for manipulating binary data.

Compatibility#

C++17

Dependencies#

  • pw_preprocessor

  • pw_status

  • pw_span

Features#

pw_bytes/alignment.h#

Functions for aligning sizes and addresses to memory alignment boundaries.

pw_bytes/array.h#

Functions for working with byte arrays, primarily for building fixed-size byte arrays at compile time.

pw_bytes/byte_builder.h#

class ByteBuilder#

ByteBuilder facilitates building bytes in a fixed-size buffer. BytesBuilders never overflow. Status is tracked for each operation and an overall status is maintained, which reflects the most recent error.

A ByteBuilder does not own the buffer it writes to. It can be used to write bytes to any buffer. The ByteBuffer template class, defined below, allocates a buffer alongside a ByteBuilder.

Subclassed by pw::ByteBuffer< kSizeBytes >

Public Functions

inline constexpr ByteBuilder(ByteSpan buffer)#

Creates an empty ByteBuilder.

ByteBuilder(const ByteBuilder&) = delete#

Disallow copy/assign to avoid confusion about where the bytes is actually stored. ByteBuffers may be copied into one another.

inline const std::byte *data() const#

Returns the contents of the bytes buffer.

inline Status status() const#

Returns the ByteBuilder’s status, which reflects the most recent error that occurred while updating the bytes. After an update fails, the status remains non-OK until it is cleared with clear() or clear_status(). Returns:

OK if no errors have occurred
RESOURCE_EXHAUSTED if output to the ByteBuilder was truncated
INVALID_ARGUMENT if printf-style formatting failed
OUT_OF_RANGE if an operation outside the buffer was attempted

inline StatusWithSize status_with_size() const#

Returns status() and size() as a StatusWithSize.

inline bool ok() const#

True if status() is OkStatus().

inline bool empty() const#

True if the bytes builder is empty.

inline size_t size() const#

Returns the current length of the bytes.

inline size_t max_size() const#

Returns the maximum length of the bytes.

inline void clear()#

Clears the bytes and resets its error state.

inline void clear_status()#

Sets the statuses to OkStatus();.

inline void push_back(std::byte b)#

Appends a single byte. Sets the status to RESOURCE_EXHAUSTED if the byte cannot be added because the buffer is full.

inline void pop_back()#

Removes the last byte. Sets the status to OUT_OF_RANGE if the buffer is empty (in which case the unsigned overflow is intentional).

inline const_iterator begin() const#

Root of bytebuffer wrapped in iterator type.

inline const_iterator end() const#

End of bytebuffer wrapped in iterator type.

inline const std::byte &front() const#

Front and Back C++ container functions.

ByteBuilder &append(size_t count, std::byte b)#

Appends the provided byte count times.

ByteBuilder &append(const void *bytes, size_t count)#

Appends count bytes from ‘bytes’ to the end of the ByteBuilder. If count exceeds the remaining space in the ByteBuffer, no bytes will be appended and the status is set to RESOURCE_EXHAUSTED.

inline ByteBuilder &append(ConstByteSpan bytes)#

Appends bytes from a byte span that calls the pointer/length version.

void resize(size_t new_size)#

Sets the ByteBuilder’s size. This function only truncates; if new_size > size(), it sets status to OUT_OF_RANGE and does nothing.

inline ByteBuilder &PutUint8(uint8_t val)#

Put methods for inserting different 8-bit ints.

inline ByteBuilder &PutUint16(uint16_t value, endian order = endian::little)#

Put methods for inserting different 16-bit ints.

inline ByteBuilder &PutUint32(uint32_t value, endian order = endian::little)#

Put methods for inserting different 32-bit ints.

inline ByteBuilder &PutUint64(uint64_t value, endian order = endian::little)#

Put methods for inserting different 64-bit ints.

class iterator#

iterator class will allow users of ByteBuilder and ByteBuffer to access the data stored in the buffer. It has the functionality of C++’s random access iterator.

Public Functions

inline int8_t PeekInt8() const#

The Peek methods will retreive ordered (Little/Big Endian) values located at the iterator position without moving the iterator forward.

inline int8_t ReadInt8()#

The Read methods will retreive ordered (Little/Big Endian) values located at the iterator position and move the iterator forward by sizeof(value) positions forward.

template<size_t kSizeBytes>
class ByteBuffer : public pw::ByteBuilder#

ByteBuffers declare a buffer along with a ByteBuilder.

Public Functions

inline ByteBuffer(const ByteBuffer &other)#

ByteBuffers of the same size may be copied and assigned into one another.

template<size_t kOtherSizeBytes>
inline ByteBuffer(const ByteBuffer<kOtherSizeBytes> &other)#

A smaller ByteBuffer may be copied or assigned into a larger one.

template<typename ...Args>
inline ByteBuffer &append(Args&&... args)#

Returns a ByteBuffer<kSizeBytes>& instead of a generic ByteBuilder& for append calls.

Public Static Functions

static inline constexpr size_t max_size()#

Returns the maximum length of the bytes that can be inserted in the bytes buffer.

Size report: using ByteBuffer#

Label

Segment

Delta

Using ByteBuilder vs not using it

FLASH

+4

_ctype_

+4

quorem

+4

pw::bytes::ReadBytes()

+20

pw::bytes::PutBytes()

+2

pw_boot_PreStaticMemoryInit

+2

main

+4

p05.0

NEW

+52

memmove

NEW

+36

pw::ByteBuilder::ResizeForAppend()

NEW

+32

pw::ByteBuilder::append()

NEW

+24

_GLOBAL__sub_I__ZN2pw5bytes2bbE

NEW

+4

pw::bytes::internal::ReverseBytes<>()

+188

pw_bytes/bit.h#

Implementation of features provided by C++20’s <bit> header. Supported features:

  • pw::endian – Implementation of the std::endian enum. If std::endian is available, pw::endian is an alias of it.

  • Additional functions for bit-level operations.

    template<std::size_t kBitWidth, typename T>
    constexpr T pw::bytes::SignExtend(T nbit_value)#

    Extends the nth bit to the left. Useful for expanding singed values into larger integer types.

pw_bytes/endian.h#

Functions for converting the endianness of integral values.

pw_bytes/suffix.h#

This module exports a single _b literal, making it easier to create std::byte values for tests.

constexpr std::byte operator""_b(unsigned long long value)#

pw_bytes/units.h#

Constants, functions and user-defined literals for specifying a number of bytes in powers of two, as defined by IEC 60027-2 A.2 and ISO/IEC 80000:13-2008.

The supported suffixes include:

  • _B for bytes (10240)

  • _KiB for kibibytes (10241)

  • _MiB for mebibytes (10242)

  • _GiB for gibibytes (10243)

  • _TiB for tebibytes (10244)

  • _PiB for pebibytes (10245)

  • _EiB for exbibytes (10246)

In order to use these you must use a using namespace directive, for example:

#include "pw_bytes/units.h"

using namespace pw::bytes::unit_literals;

constexpr size_t kRandomBufferSizeBytes = 1_MiB + 42_KiB;

In some cases, the use of user-defined literals is not permitted because of the required using namespace directive. One example of this is in header files, where it is undesirable to pollute the namespace. For this situation, there are also similar functions:

#include "pw_bytes/units.h"

constexpr size_t kBufferSizeBytes = pw::bytes::MiB(1) + pw::bytes::KiB(42);

Zephyr#

To enable pw_bytes for Zephyr add CONFIG_PIGWEED_BYTES=y to the project’s configuration.