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3396c97da9
Now that the new CMake build system is encouraging us to lay out the code like a set of libraries, it seems like a good idea to make them look more _like_ libraries, by putting things into separate modules as far as possible. This fixes several previous annoyances in which you had to link against some object in order to get a function you needed, but that object also contained other functions you didn't need which included link-time symbol references you didn't want to have to deal with. The usual offender was subsidiary supporting programs including misc.c for some innocuous function and then finding they had to deal with the requirements of buildinfo(). This big reorganisation introduces three new subdirectories called 'utils', one at the top level and one in each platform subdir. In each case, the directory contains basically the same files that were previously placed in the 'utils' build-time library, except that the ones that were extremely miscellaneous (misc.c, utils.c, uxmisc.c, winmisc.c, winmiscs.c, winutils.c) have been split up into much smaller pieces.
26 lines
814 B
C
26 lines
814 B
C
/*
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* Compare two fixed-size regions of memory, in a crypto-safe way,
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* i.e. without timing or cache side channels indicating anything
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* about what the answer was or where the first difference (if any)
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* might have been.
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*/
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#include "defs.h"
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#include "misc.h"
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bool smemeq(const void *av, const void *bv, size_t len)
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{
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const unsigned char *a = (const unsigned char *)av;
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const unsigned char *b = (const unsigned char *)bv;
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unsigned val = 0;
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while (len-- > 0) {
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val |= *a++ ^ *b++;
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}
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/* Now val is 0 iff we want to return 1, and in the range
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* 0x01..0xFF iff we want to return 0. So subtracting from 0x100
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* will clear bit 8 iff we want to return 0, and leave it set iff
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* we want to return 1, so then we can just shift down. */
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return (0x100 - val) >> 8;
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}
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