MEMORY(2)                                               MEMORY(2)

     NAME
          memccpy, memchr, memcmp, memcpy, memmove, memset, tsmemcmp -
          memory operations

     SYNOPSIS
          #include <u.h>
          #include <libc.h>

          void* memccpy(void *s1, void *s2, int c, usize n)

          void* memchr(void *s, int c, usize n)

          int   memcmp(void *s1, void *s2, usize n)

          void* memcpy(void *s1, void *s2, usize n)

          void* memmove(void *s1, void *s2, usize n)

          void* memset(void *s, int c, usize n)

          #include <libsec.h>

          int   tsmemcmp(void *s1, void *s2, ulong n)

     DESCRIPTION
          These functions operate efficiently on memory areas (arrays
          of bytes bounded by a count, not terminated by a zero byte).
          They do not check for the overflow of any receiving memory
          area.

          Memccpy copies bytes from memory area s2 into s1, stopping
          after the first occurrence of byte c has been copied, or
          after n bytes have been copied, whichever comes first.  It
          returns a pointer to the byte after the copy of c in s1, or
          zero if c was not found in the first n bytes of s2.

          Memchr returns a pointer to the first occurrence of byte c
          in the first n bytes of memory area s, or zero if c does not
          occur.

          Memcmp compares its arguments, looking at the first n bytes
          only, and returns an integer less than, equal to, or greater
          than 0, according as s1 is lexicographically less than,
          equal to, or greater than s2. The comparison is bytewise
          unsigned.

          Memcpy copies n bytes from memory area s2 to s1. It returns
          s1.

          Memmove works like memcpy, except that it is guaranteed to

     Page 1                       Plan 9            (printed 10/28/25)

     MEMORY(2)                                               MEMORY(2)

          work if s1 and s2 overlap.

          Memset sets the first n bytes in memory area s to the value
          of byte c. It returns s.

          Tsmemcmp is a variant of memcmp that is safe against timing
          attacks.  It does not stop when it sees a difference, this
          way it's runtime is function of n and not something that can
          lead clues to attackers.

     SOURCE
          All these routines have portable C implementations in
          /sys/src/libc/port.  Most also have machine-dependent assem-
          bly language implementations in /sys/src/libc/$objtype.
          Tsmemcmp is found on /sys/src/libsec/port/tsmemcmp.c.

     SEE ALSO
          strcat(2)

     BUGS
          ANSI C does not require memcpy to handle overlapping source
          and destination; on Plan 9, it does, so memmove and memcpy
          behave identically.

          If memcpy and memmove are handed a negative count, they
          abort.

          Memcmp should not be used to compare sensitive data as it's
          vulnerable to timing attacks. Instead, tsmemcmp should be
          used.

     Page 2                       Plan 9            (printed 10/28/25)