strlen.s revision 2
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25cf1a301a396c38e8adf52c15f537b80d2483f7jl * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * Use is subject to license terms.
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * strlen(s)
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * Given string s, return length (not including the terminating null).
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * Fast assembler language version of the following C-program strlen
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * which represents the `standard' for the C-library.
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * strlen(s)
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * register const char *s;
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * register const char *s0 = s + 1;
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * while (*s++ != '\0')
25cf1a301a396c38e8adf52c15f537b80d2483f7jl * return (s - s0);
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! The object of strlen is to, as quickly as possible, find the
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! null byte. To this end, we attempt to get our string aligned
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! and then blast across it using Alan Mycroft's algorithm for
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! finding null bytes. If we are not aligned, the string is
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! checked a byte at a time until it is. Once this occurs,
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! we can proceed word-wise across it. Once a word with a
25cf1a301a396c38e8adf52c15f537b80d2483f7jl ! zero byte has been found, we then check the word a byte