[m-rev.] for review: Simplify string.between implementation.

[Mark Brown]

This looks fine.

On Wed, Oct 23, 2019 at 3:03 PM Peter Wang <novalazy at gmail.com> wrote:
>
> library/string.m:
>     Replace foreign code implementations with Mercury code.
> ---
>  library/string.m | 113 ++++++-----------------------------------------
>  1 file changed, 14 insertions(+), 99 deletions(-)
>
> diff --git a/library/string.m b/library/string.m
> index a02a4ebab..c978476ab 100644
> --- a/library/string.m
> +++ b/library/string.m
> @@ -4200,108 +4200,23 @@ right_by_codepoint(String, RightCount, RightString) :-
>  between(Str, Start, End) = SubString :-
>      between(Str, Start, End, SubString).
>
> -:- pragma foreign_proc("C",
> -    between(Str::in, Start::in, End::in, SubString::uo),
> -    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
> -        does_not_affect_liveness, may_not_duplicate, no_sharing],
> -"{
> -    MR_Integer  len;
> -    MR_Integer  Count;
> -
> -    if (Start < 0) Start = 0;
> -    if (End <= Start) {
> -        MR_make_aligned_string(SubString, """");
> -    } else {
> -        len = strlen(Str);
> -        if (Start > len) {
> -            Start = len;
> -        }
> -        if (End > len) {
> -            End = len;
> -        }
> -        Count = End - Start;
> -        MR_allocate_aligned_string_msg(SubString, Count, MR_ALLOC_ID);
> -        MR_memcpy(SubString, Str + Start, Count);
> -        SubString[Count] = '\\0';
> -    }
> -}").
> -:- pragma foreign_proc("C#",
> -    between(Str::in, Start::in, End::in, SubString::uo),
> -    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
> -        does_not_affect_liveness, may_not_duplicate, no_sharing],
> -"
> -    if (Start < 0) Start = 0;
> -    if (End <= Start) {
> -        SubString = """";
> -    } else {
> -        int len = Str.Length;
> -        if (Start > len) {
> -            Start = len;
> -        }
> -        if (End > len) {
> -            End = len;
> -        }
> -        SubString = Str.Substring(Start, End - Start);
> -    }
> -").
> -:- pragma foreign_proc("Java",
> -    between(Str::in, Start::in, End::in, SubString::uo),
> -    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
> -        does_not_affect_liveness, may_not_duplicate, no_sharing],
> -"
> -    if (Start < 0) Start = 0;
> -    if (End <= Start) {
> -        SubString = """";
> -    } else {
> -        int len = Str.length();
> -        if (Start > len) {
> -            Start = len;
> -        }
> -        if (End > len) {
> -            End = len;
> -        }
> -        SubString = Str.substring(Start, End);
> -    }
> -").
> -:- pragma foreign_proc("Erlang",
> -    between(Str::in, Start0::in, End0::in, SubString::uo),
> -    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
> -        does_not_affect_liveness],
> -"
> -    Start = max(Start0, 0),
> -    End = min(End0, size(Str)),
> -    Count = End - Start,
> -    if Count =< 0 ->
> -        SubString = <<>>
> -    ; true ->
> -        <<_:Start/binary, SubString:Count/binary, _/binary>> = Str
> -    end
> -").
> -
>  between(Str, Start, End, SubStr) :-
> -    ( if Start >= End then
> -        SubStr = ""
> +    Len = length(Str),
> +    ( if Start =< 0 then
> +        ClampStart = 0
> +    else if Start >= Len then
> +        ClampStart = Len
>      else
> -        Len = length(Str),
> -        max(0, Start, ClampStart),
> -        min(Len, End, ClampEnd),
> -        CharList = between_loop(ClampStart, ClampEnd, Str),
> -        SubStr = from_char_list(CharList)
> -    ).
> -
> -:- func between_loop(int, int, string) = list(char).
> -
> -between_loop(I, End, Str) = Chars :-
> -    ( if
> -        I < End,
> -        unsafe_index_next(Str, I, J, C),
> -        J =< End
> -    then
> -        Cs = between_loop(J, End, Str),
> -        Chars = [C | Cs]
> +        ClampStart = Start
> +    ),
> +    ( if End =< ClampStart then
> +        ClampEnd = ClampStart
> +    else if End >= Len then
> +        ClampEnd = Len
>      else
> -        Chars = []
> -    ).
> +        ClampEnd = End
> +    ),
> +    unsafe_between(Str, ClampStart, ClampEnd, SubStr).
>
>  %---------------------%
>
> --
> 2.23.0
>
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