[libc-commits] [libc] [libc] Implement strftime (PR #111305)

[Tsz Chan via libc-commits]

tszhin-swe wrote:

Sorry I missed that, I would make sure to be clear about licensing issues
before making other PRs.

On Thu, 9 Jan 2025 at 7:26 AM, Michael Jones ***@***.***>
wrote:

> ***@***.**** commented on this pull request.
> ------------------------------
>
> In libc/src/time/strftime_core/num_converter.h
> <https://github.com/llvm/llvm-project/pull/111305#discussion_r1907948397>:
>
> > +LIBC_INLINE bool is_leap(int year) {
> +  return ((year % 4 == 0) && (year % 100 != 0 || year % 400 == 0));
> +}
> +
> +static int iso_week_days(int yday, int wday) {
> +  /* Add enough to the first operand of % to make it nonnegative.  */
> +  int big_enough_multiple_of_7 = (-YDAY_MINIMUM / 7 + 2) * 7;
> +  return (yday - (yday - wday + ISO_WEEK1_WDAY + big_enough_multiple_of_7) % 7 +
> +          ISO_WEEK1_WDAY - ISO_WEEK_START_WDAY);
> +}
> +
> +enum class IsoData {
> +  GET_DATE,
> +  GET_YEAR,
> +};
> +
> +template <IsoData get_date_or_year>
> +LIBC_INLINE int convert_iso(const FormatSection &to_conv) {
> +  int year = to_conv.time->tm_year + YEAR_BASE;
> +  int days = iso_week_days(to_conv.time->tm_yday, to_conv.time->tm_wday);
> +
> +  if (days < 0) {
> +    /* This ISO week belongs to the previous year.  */
> +    year--;
> +    days = iso_week_days(to_conv.time->
>
> tm_yday + (365 + is_leap(year)),
> +                         to_conv.time->tm_wday);
> +  } else {
> +    int d = iso_week_days(to_conv.time->tm_yday - (365 + is_leap(year)),
> +                          to_conv.time->tm_wday);
> +    if (0 <= d) {
> +      /* This ISO week belongs to the next year.  */
> +      year++;
> +      days = d;
> +    }
> +  }
>
> This section of code is copied from glibc:
> https://github.com/bminor/glibc/blob/master/time/strftime_l.c#L383
>
> That's not acceptable both for licensing and for plagiarism reasons.
> Copying code from other projects - even open source ones - can cause
> significant legal issues. The license glibc uses is called the "LGPL" and
> the license LLVM uses is based on the "Apache License". I'd recommend at
> least researching both of these before making any more PRs.
>
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https://github.com/llvm/llvm-project/pull/111305