Date: Wed, 4 Mar 2020 12:06:21 +0300 (MSK) From: Alexander Monakov <amonakov@...ras.ru> To: musl@...ts.openwall.com cc: Timo Teräs <timo.teras@....fi> Subject: Re: [PATCH] improve strerror speed Hi, On Tue, 3 Mar 2020, Timo Teräs wrote: > change the current O(n) lookup to O(1) based on the machinery > described in "How To Write Shared Libraries" (Appendix B). I'm curious about the background of this change, did the inefficiency came up in practice? > --- a/src/errno/__strerror.h > +++ b/src/errno/__strerror.h > @@ -1,8 +1,9 @@ > -/* This file is sorted such that 'errors' which represent exceptional > - * conditions under which a correct program may fail come first, followed > - * by messages that indicate an incorrect program or system failure. The > - * macro E() along with double-inclusion is used to ensure that ordering > - * of the strings remains synchronized. */ > +/* The first '0' mapping will be used for error codes that > + * are not explicitly mentioned here. > + * This file is included multiple times to generate struct > + * populate it's content and create a fast lookup index to it. */ The last sentence seems to have typos ("a struct,", "its"). I would write the comment like this: /* The first entry is a catch-all for codes not enumerated here. * This file is included multiple times to declare and define a structure * with messages, and then to define a lookup table translating error codes * to offsets of corresponding fields in the structure. */ > + if (e < 0 || e >= sizeof(errmsgidx)/sizeof(errmsgidx)) e = 0; I think usually in musl such range checks are written in an easier-to-optimize form that tests the argument in an unsigned type, e.g. like this: if ((size_t)e >= sizeof errmsgidx / sizeof *errmsgidx) e = 0; Thanks. Alexander
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