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Re: [PATCH] strftime: support %q to output the quarter of year

From: Paul Eggert <eggert at cs dot ucla dot edu>
To: Pádraig Brady <P at draigBrady dot com>, libc-alpha at sourceware dot org
Date: Thu, 3 Nov 2016 21:12:27 -0700
Subject: Re: [PATCH] strftime: support %q to output the quarter of year
Authentication-results: sourceware.org; auth=none
References: <1478202401-5238-1-git-send-email-P@draigBrady.com> <c16c3a8b-857a-5109-6500-4cfebd86606d@draigBrady.com>

Pádraig Brady wrote:

+          DO_NUMBER (1, tp->tm_mon / 3 + 1);

I couldn't resist puzzling this one out. We can assume 0 <= tp->tm_mon < 12, sothis should be a tad more efficient:


   DO_NUMBER (1, ((tp->tm_mon * 11) >> 5) + 1);

With gcc 6.2.0 -O2 x86-64, the former uses imull with 6 insns, the latter justleal with 4 insns. Perhaps GCC should be smart enough to figure this out on itsown, but what would be the fun of that?

References:
- [PATCH] strftime: support %q to output the quarter of year
  - From: Pádraig Brady
- Re: [PATCH] strftime: support %q to output the quarter of year
  - From: Pádraig Brady

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