mirror of
https://github.com/torvalds/linux.git
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1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
253 lines
8.2 KiB
C
253 lines
8.2 KiB
C
/*#************************************************************************#*/
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/*#-------------------------------------------------------------------------*/
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/*# */
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/*# FUNCTION NAME: memset() */
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/*# */
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/*# PARAMETERS: void* dst; Destination address. */
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/*# int c; Value of byte to write. */
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/*# int len; Number of bytes to write. */
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/*# */
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/*# RETURNS: dst. */
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/*# */
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/*# DESCRIPTION: Sets the memory dst of length len bytes to c, as standard. */
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/*# Framework taken from memcpy. This routine is */
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/*# very sensitive to compiler changes in register allocation. */
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/*# Should really be rewritten to avoid this problem. */
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/*# */
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/*#-------------------------------------------------------------------------*/
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/*# */
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/*# HISTORY */
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/*# */
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/*# DATE NAME CHANGES */
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/*# ---- ---- ------- */
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/*# 990713 HP Tired of watching this function (or */
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/*# really, the nonoptimized generic */
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/*# implementation) take up 90% of simulator */
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/*# output. Measurements needed. */
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/*# */
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/*#-------------------------------------------------------------------------*/
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#include <linux/types.h>
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/* No, there's no macro saying 12*4, since it is "hard" to get it into
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the asm in a good way. Thus better to expose the problem everywhere.
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*/
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/* Assuming 1 cycle per dword written or read (ok, not really true), and
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one per instruction, then 43+3*(n/48-1) <= 24+24*(n/48-1)
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so n >= 45.7; n >= 0.9; we win on the first full 48-byte block to set. */
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#define ZERO_BLOCK_SIZE (1*12*4)
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void *memset(void *pdst,
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int c,
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size_t plen)
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{
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/* Ok. Now we want the parameters put in special registers.
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Make sure the compiler is able to make something useful of this. */
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register char *return_dst __asm__ ("r10") = pdst;
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register int n __asm__ ("r12") = plen;
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register int lc __asm__ ("r11") = c;
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/* Most apps use memset sanely. Only those memsetting about 3..4
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bytes or less get penalized compared to the generic implementation
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- and that's not really sane use. */
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/* Ugh. This is fragile at best. Check with newer GCC releases, if
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they compile cascaded "x |= x << 8" sanely! */
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__asm__("movu.b %0,$r13\n\t"
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"lslq 8,$r13\n\t"
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"move.b %0,$r13\n\t"
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"move.d $r13,%0\n\t"
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"lslq 16,$r13\n\t"
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"or.d $r13,%0"
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: "=r" (lc) : "0" (lc) : "r13");
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{
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register char *dst __asm__ ("r13") = pdst;
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/* This is NONPORTABLE, but since this whole routine is */
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/* grossly nonportable that doesn't matter. */
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if (((unsigned long) pdst & 3) != 0
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/* Oops! n=0 must be a legal call, regardless of alignment. */
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&& n >= 3)
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{
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if ((unsigned long)dst & 1)
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{
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*dst = (char) lc;
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n--;
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dst++;
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}
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if ((unsigned long)dst & 2)
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{
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*(short *)dst = lc;
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n -= 2;
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dst += 2;
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}
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}
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/* Now the fun part. For the threshold value of this, check the equation
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above. */
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/* Decide which copying method to use. */
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if (n >= ZERO_BLOCK_SIZE)
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{
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/* For large copies we use 'movem' */
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/* It is not optimal to tell the compiler about clobbering any
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registers; that will move the saving/restoring of those registers
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to the function prologue/epilogue, and make non-movem sizes
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suboptimal.
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This method is not foolproof; it assumes that the "asm reg"
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declarations at the beginning of the function really are used
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here (beware: they may be moved to temporary registers).
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This way, we do not have to save/move the registers around into
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temporaries; we can safely use them straight away.
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If you want to check that the allocation was right; then
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check the equalities in the first comment. It should say
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"r13=r13, r12=r12, r11=r11" */
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__asm__ volatile ("
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;; Check that the following is true (same register names on
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;; both sides of equal sign, as in r8=r8):
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;; %0=r13, %1=r12, %4=r11
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;;
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;; Save the registers we'll clobber in the movem process
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;; on the stack. Don't mention them to gcc, it will only be
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;; upset.
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subq 11*4,$sp
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movem $r10,[$sp]
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move.d $r11,$r0
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move.d $r11,$r1
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move.d $r11,$r2
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move.d $r11,$r3
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move.d $r11,$r4
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move.d $r11,$r5
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move.d $r11,$r6
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move.d $r11,$r7
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move.d $r11,$r8
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move.d $r11,$r9
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move.d $r11,$r10
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;; Now we've got this:
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;; r13 - dst
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;; r12 - n
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;; Update n for the first loop
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subq 12*4,$r12
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0:
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subq 12*4,$r12
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bge 0b
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movem $r11,[$r13+]
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addq 12*4,$r12 ;; compensate for last loop underflowing n
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;; Restore registers from stack
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movem [$sp+],$r10"
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/* Outputs */ : "=r" (dst), "=r" (n)
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/* Inputs */ : "0" (dst), "1" (n), "r" (lc));
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}
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/* Either we directly starts copying, using dword copying
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in a loop, or we copy as much as possible with 'movem'
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and then the last block (<44 bytes) is copied here.
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This will work since 'movem' will have updated src,dst,n. */
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while ( n >= 16 )
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{
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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n -= 16;
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}
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/* A switch() is definitely the fastest although it takes a LOT of code.
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* Particularly if you inline code this.
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*/
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switch (n)
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{
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case 0:
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break;
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case 1:
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*(char*)dst = (char) lc;
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break;
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case 2:
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*(short*)dst = (short) lc;
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break;
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case 3:
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*((short*)dst)++ = (short) lc;
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*(char*)dst = (char) lc;
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break;
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case 4:
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*((long*)dst)++ = lc;
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break;
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case 5:
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*((long*)dst)++ = lc;
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*(char*)dst = (char) lc;
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break;
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case 6:
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*((long*)dst)++ = lc;
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*(short*)dst = (short) lc;
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break;
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case 7:
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*((long*)dst)++ = lc;
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*((short*)dst)++ = (short) lc;
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*(char*)dst = (char) lc;
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break;
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case 8:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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break;
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case 9:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*(char*)dst = (char) lc;
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break;
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case 10:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*(short*)dst = (short) lc;
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break;
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case 11:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((short*)dst)++ = (short) lc;
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*(char*)dst = (char) lc;
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break;
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case 12:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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break;
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case 13:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*(char*)dst = (char) lc;
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break;
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case 14:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*(short*)dst = (short) lc;
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break;
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case 15:
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((long*)dst)++ = lc;
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*((short*)dst)++ = (short) lc;
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*(char*)dst = (char) lc;
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break;
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}
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}
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return return_dst; /* destination pointer. */
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} /* memset() */
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