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Thu, 02 Jul 2026 02:30:11 -0700 (PDT) Message-ID: <7bed7164-9a53-4e53-9fc1-7af68108bdf8@suse.com> Date: Thu, 2 Jul 2026 11:30:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PATCH v2 2/4] time: shorten year determination loop From: Jan Beulich To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: <79d50725-3892-4643-b854-bfec9c0c0d79@suse.com> Content-Language: en-US Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <79d50725-3892-4643-b854-bfec9c0c0d79@suse.com> Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-ebf023/1782984612-AE3371CC-6FE7A245/0/0 X-purgate-type: clean X-purgate-size: 1420 X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1782984633593158500 Content-Type: text/plain; charset="utf-8" For dates very far into the future (the MC146818 RTC's century byte can go up to the 99th century), the present year-wise loop would become somewhat inefficient (taking perhaps several thousand iterations). Prefix that loop with a 400-year granular calculation (somewhat like the earlier loop does for dates in the past). Signed-off-by: Jan Beulich --- v2: New. --- a/xen/common/time.c +++ b/xen/common/time.c @@ -27,6 +27,8 @@ #define __isleap(year) \ ((year) % 4 =3D=3D 0 && ((year) % 100 !=3D 0 || (year) % 400 =3D=3D 0)) =20 +#define DAYS_IN_400_YEARS (365 * 303 + 366 * 97) + /* How many days are in each month. */ static const unsigned short int __mon_lengths[2][12] =3D { /* Normal years. */ @@ -57,7 +59,7 @@ struct tm gmtime(unsigned long t) while ( t & (1UL<<39) ) { y -=3D 400; - t +=3D ((unsigned long)(365 * 303 + 366 * 97)) * SECS_PER_DAY; + t +=3D (unsigned long)DAYS_IN_400_YEARS * SECS_PER_DAY; } t &=3D (1UL << 40) - 1; #endif @@ -71,6 +73,11 @@ struct tm gmtime(unsigned long t) tbuf.tm_sec =3D rem % 60; /* January 1, 1970 was a Thursday. */ tbuf.tm_wday =3D (4 + days) % 7; + if ( days >=3D DAYS_IN_400_YEARS ) + { + y +=3D (days / DAYS_IN_400_YEARS) * 400; + days %=3D DAYS_IN_400_YEARS; + } while ( days >=3D (rem =3D __isleap(y) ? 366 : 365) ) { ++y;