Module Bigstringaf

Bigstrings, but fast.

The OCaml compiler has a bunch of intrinsics for Bigstrings, but they're not widely-known, sometimes misused, and so programs that use Bigstrings are slower than they have to be. And even if a library got that part right and exposed the intrinsics properly, the compiler doesn't have any fast blits between Bigstrings and other string-like types.

So here they are. Go crazy.

type t = (char, Bigarray_compat.int8_unsigned_elt, Bigarray_compat.c_layout) Bigarray_compat.Array1.t

Constructors

val create : int -> t

create n returns a bigstring of length n

val empty : t

empty is the empty bigstring. It has length 0 and you can't really do much with it, but it's a good placeholder that only needs to be allocated once.

val of_string : off:int -> len:int -> string -> t

of_string ~off ~len s returns a bigstring of length len that contains the contents of string from the range [off, len).

val copy : t -> off:int -> len:int -> t

copy t ~off ~len allocates a new bigstring of length len and copies the bytes from t copied into it starting from off.

val sub : t -> off:int -> len:int -> t

sub t ~off ~len does not allocate a bigstring, but instead returns a new view into t starting at off, and with length len.

Note that this does not allocate a new buffer, but instead shares the buffer of t with the newly-returned bigstring.

Memory-safe Operations

val length : t -> int

length t is the length of the bigstring, in bytes.

val substring : t -> off:int -> len:int -> string

substring t ~off ~len returns a string of length len containing the bytes of t starting at off.

val to_string : t -> string

to_string t is equivalent to substring t ~off:0 ~len:(length t)

val get : t -> int -> char

get t i returns the character at offset i in t.

val set : t -> int -> char -> unit

set t i c sets the character at offset i in t to be c

Little-endian Byte Order

The following operations assume a little-endian byte ordering of the bigstring. If the machine-native byte ordering differs, then the get operations will reorder the bytes so that they are in machine-native byte order before returning the result, and the set operations will reorder the bytes so that they are written out in the appropriate order.

Most modern processor architectures are little-endian, so more likely than not, these operations will not do any byte reordering.

val get_int16_le : t -> int -> int

get_int16_le t i returns the two bytes in t starting at offset i, interpreted as an unsigned integer.

val get_int16_sign_extended_le : t -> int -> int

get_int16_sign_extended_le t i returns the two bytes in t starting at offset i, interpreted as a signed integer and performing sign extension to the native word size before returning the result.

val set_int16_le : t -> int -> int -> unit

set_int16_le t i v sets the two bytes in t starting at offset i to the value v.

val get_int32_le : t -> int -> int32

get_int32_le t i returns the four bytes in t starting at offset i.

val set_int32_le : t -> int -> int32 -> unit

set_int32_le t i v sets the four bytes in t starting at offset i to the value v.

val get_int64_le : t -> int -> int64

get_int64_le t i returns the eight bytes in t starting at offset i.

val set_int64_le : t -> int -> int64 -> unit

set_int64_le t i v sets the eight bytes in t starting at offset i to the value v.

Big-endian Byte Order

The following operations assume a big-endian byte ordering of the bigstring. If the machine-native byte ordering differs, then the get operations will reorder the bytes so that they are in machine-native byte order before returning the result, and the set operations will reorder the bytes so that they are written out in the appropriate order.

Network byte order is big-endian, so you may need these operations when dealing with raw frames, for example, in a userland networking stack.

val get_int16_be : t -> int -> int

get_int16_be t i returns the two bytes in t starting at offset i, interpreted as an unsigned integer.

val get_int16_sign_extended_be : t -> int -> int

get_int16_sign_extended_be t i returns the two bytes in t starting at offset i, interpreted as a signed integer and performing sign extension to the native word size before returning the result.

val set_int16_be : t -> int -> int -> unit

set_int16_be t i v sets the two bytes in t starting at offset off to the value v.

val get_int32_be : t -> int -> int32

get_int32_be t i returns the four bytes in t starting at offset i.

val set_int32_be : t -> int -> int32 -> unit

set_int32_be t i v sets the four bytes in t starting at offset i to the value v.

val get_int64_be : t -> int -> int64

get_int64_be t i returns the eight bytes in t starting at offset i.

val set_int64_be : t -> int -> int64 -> unit

set_int64_be t i v sets the eight bytes in t starting at offset i to the value v.

Blits

All the following blit operations do the same thing. They copy a given number of bytes from a source starting at some offset to a destination starting at some other offset. Forgetting for a moment that OCaml is a memory-safe language, these are all equivalent to:

memcpy(dst + dst_off, src + src_off, len);

And in fact, that's how they're implemented. Except that bounds checking is performed before performing the blit.

val blit : t -> src_off:int -> t -> dst_off:int -> len:int -> unit
val blit_from_string : string -> src_off:int -> t -> dst_off:int -> len:int -> unit
val blit_from_bytes : Stdlib.Bytes.t -> src_off:int -> t -> dst_off:int -> len:int -> unit
val blit_to_bytes : t -> src_off:int -> Stdlib.Bytes.t -> dst_off:int -> len:int -> unit

memcmp

Fast comparisons based on memcmp. Similar to the blits, these are implemented as C calls after performing bounds checks.

memcmp(buf1 + off1, buf2 + off2, len);
val memcmp : t -> int -> t -> int -> int -> int
val memcmp_string : t -> int -> string -> int -> int -> int

Memory-unsafe Operations

The following operations are not memory safe. However, they do compile down to just a couple instructions. Make sure when using them to perform your own bounds checking. Or don't. Just make sure you know what you're doing. You can do it, but only do it if you have to.

val unsafe_get : t -> int -> char

unsafe_get t i is like get except no bounds checking is performed.

val unsafe_set : t -> int -> char -> unit

unsafe_set t i c is like set except no bounds checking is performed.

val unsafe_get_int16_le : t -> int -> int

unsafe_get_int16_le t i is like get_int16_le except no bounds checking is performed.

val unsafe_get_int16_be : t -> int -> int

unsafe_get_int16_be t i is like get_int16_be except no bounds checking is performed.

val unsafe_get_int16_sign_extended_le : t -> int -> int

unsafe_get_int16_sign_extended_le t i is like get_int16_sign_extended_le except no bounds checking is performed.

val unsafe_get_int16_sign_extended_be : t -> int -> int

unsafe_get_int16_sign_extended_be t i is like get_int16_sign_extended_be except no bounds checking is performed.

val unsafe_set_int16_le : t -> int -> int -> unit

unsafe_set_int16_le t i v is like set_int16_le except no bounds checking is performed.

val unsafe_set_int16_be : t -> int -> int -> unit

unsafe_set_int16_be t i v is like set_int16_be except no bounds checking is performed.

val unsafe_get_int32_le : t -> int -> int32

unsafe_get_int32_le t i is like get_int32_le except no bounds checking is performed.

val unsafe_get_int32_be : t -> int -> int32

unsafe_get_int32_be t i is like get_int32_be except no bounds checking is performed.

val unsafe_set_int32_le : t -> int -> int32 -> unit

unsafe_set_int32_le t i v is like set_int32_le except no bounds checking is performed.

val unsafe_set_int32_be : t -> int -> int32 -> unit

unsafe_set_int32_be t i v is like set_int32_be except no bounds checking is performed.

val unsafe_get_int64_le : t -> int -> int64

unsafe_get_int64_le t i is like get_int64_le except no bounds checking is performed.

val unsafe_get_int64_be : t -> int -> int64

unsafe_get_int64_be t i is like get_int64_be except no bounds checking is performed.

val unsafe_set_int64_le : t -> int -> int64 -> unit

unsafe_set_int64_le t i v is like set_int64_le except no bounds checking is performed.

val unsafe_set_int64_be : t -> int -> int64 -> unit

unsafe_set_int64_be t i v is like set_int64_be except no bounds checking is performed.

Blits

All the following blit operations do the same thing. They copy a given number of bytes from a source starting at some offset to a destination starting at some other offset. Forgetting for a moment that OCaml is a memory-safe language, these are all equivalent to:

memcpy(dst + dst_off, src + src_off, len);

And in fact, that's how they're implemented. Except in the case of unsafe_blit which uses a memmove so that overlapping blits behave as expected. But in both cases, there's no bounds checking.

val unsafe_blit : t -> src_off:int -> t -> dst_off:int -> len:int -> unit
val unsafe_blit_from_string : string -> src_off:int -> t -> dst_off:int -> len:int -> unit
val unsafe_blit_from_bytes : Stdlib.Bytes.t -> src_off:int -> t -> dst_off:int -> len:int -> unit
val unsafe_blit_to_bytes : t -> src_off:int -> Stdlib.Bytes.t -> dst_off:int -> len:int -> unit

memcmp

Fast comparisons based on memcmp. Similar to the blits, these are not memory safe and are implemented by the same C call:

memcmp(buf1 + off1, buf2 + off2, len);
val unsafe_memcmp : t -> int -> t -> int -> int -> int
val unsafe_memcmp_string : t -> int -> string -> int -> int -> int