arch/xtensa/lib/memset.S

   1 /*
   2  *  arch/xtensa/lib/memset.S
   3  *
   4  *  ANSI C standard library function memset
   5  *  (Well, almost.  .fixup code might return zero.)
   6  *
   7  *  This file is subject to the terms and conditions of the GNU General
   8  *  Public License.  See the file "COPYING" in the main directory of
   9  *  this archive for more details.
  10  *
  11  *  Copyright (C) 2002 Tensilica Inc.
  12  */
  13
  14 #include <variant/core.h>
  15
  16 /*
  17  * void *memset(void *dst, int c, size_t length)
  18  *
  19  * The algorithm is as follows:
  20  *   Create a word with c in all byte positions
  21  *   If the destination is aligned,
  22  *     do 16B chucks with a loop, and then finish up with
  23  *     8B, 4B, 2B, and 1B stores conditional on the length.
  24  *   If destination is unaligned, align it by conditionally
  25  *     setting 1B and 2B and then go to aligned case.
  26  *   This code tries to use fall-through branches for the common
  27  *     case of an aligned destination (except for the branches to
  28  *     the alignment labels).
  29  */
  30
  31 /* Load or store instructions that may cause exceptions use the EX macro. */
  32
  33 #define EX(insn,reg1,reg2,offset,handler)       \
  34 9:      insn    reg1, reg2, offset;             \
  35         .section __ex_table, "a";               \
  36         .word   9b, handler;                    \
  37         .previous
  38
  39
  40 .text
  41 .align  4
  42 .global memset
  43 .type   memset,@function
  44 memset:
  45         entry   sp, 16          # minimal stack frame
  46         # a2/ dst, a3/ c, a4/ length
  47         extui   a3, a3, 0, 8    # mask to just 8 bits
  48         slli    a7, a3, 8       # duplicate character in all bytes of word
  49         or      a3, a3, a7      # ...
  50         slli    a7, a3, 16      # ...
  51         or      a3, a3, a7      # ...
  52         mov     a5, a2          # copy dst so that a2 is return value
  53         movi    a6, 3           # for alignment tests
  54         bany    a2, a6, .Ldstunaligned # if dst is unaligned
  55 .L0:    # return here from .Ldstunaligned when dst is aligned
  56         srli    a7, a4, 4       # number of loop iterations with 16B
  57                                 # per iteration
  58         bnez    a4, .Laligned
  59         retw
  60
  61 /*
  62  * Destination is word-aligned.
  63  */
  64         # set 16 bytes per iteration for word-aligned dst
  65         .align  4               # 1 mod 4 alignment for LOOPNEZ
  66         .byte   0               # (0 mod 4 alignment for LBEG)
  67 .Laligned:
  68 #if XCHAL_HAVE_LOOPS
  69         loopnez a7, .Loop1done
  70 #else /* !XCHAL_HAVE_LOOPS */
  71         beqz    a7, .Loop1done
  72         slli    a6, a7, 4
  73         add     a6, a6, a5      # a6 = end of last 16B chunk
  74 #endif /* !XCHAL_HAVE_LOOPS */
  75 .Loop1:
  76         EX(s32i, a3, a5,  0, memset_fixup)
  77         EX(s32i, a3, a5,  4, memset_fixup)
  78         EX(s32i, a3, a5,  8, memset_fixup)
  79         EX(s32i, a3, a5, 12, memset_fixup)
  80         addi    a5, a5, 16
  81 #if !XCHAL_HAVE_LOOPS
  82         blt     a5, a6, .Loop1
  83 #endif /* !XCHAL_HAVE_LOOPS */
  84 .Loop1done:
  85         bbci.l  a4, 3, .L2
  86         # set 8 bytes
  87         EX(s32i, a3, a5,  0, memset_fixup)
  88         EX(s32i, a3, a5,  4, memset_fixup)
  89         addi    a5, a5,  8
  90 .L2:
  91         bbci.l  a4, 2, .L3
  92         # set 4 bytes
  93         EX(s32i, a3, a5,  0, memset_fixup)
  94         addi    a5, a5,  4
  95 .L3:
  96         bbci.l  a4, 1, .L4
  97         # set 2 bytes
  98         EX(s16i, a3, a5,  0, memset_fixup)
  99         addi    a5, a5,  2
 100 .L4:
 101         bbci.l  a4, 0, .L5
 102         # set 1 byte
 103         EX(s8i, a3, a5,  0, memset_fixup)
 104 .L5:
 105 .Lret1:
 106         retw
 107
 108 /*
 109  * Destination is unaligned
 110  */
 111
 112 .Ldstunaligned:
 113         bltui   a4, 8, .Lbyteset        # do short copies byte by byte
 114         bbci.l  a5, 0, .L20             # branch if dst alignment half-aligned
 115         # dst is only byte aligned
 116         # set 1 byte
 117         EX(s8i, a3, a5,  0, memset_fixup)
 118         addi    a5, a5,  1
 119         addi    a4, a4, -1
 120         # now retest if dst aligned
 121         bbci.l  a5, 1, .L0      # if now aligned, return to main algorithm
 122 .L20:
 123         # dst half-aligned
 124         # set 2 bytes
 125         EX(s16i, a3, a5,  0, memset_fixup)
 126         addi    a5, a5,  2
 127         addi    a4, a4, -2
 128         j       .L0             # dst is now aligned, return to main algorithm
 129
 130 /*
 131  * Byte by byte set
 132  */
 133         .align  4
 134         .byte   0               # 1 mod 4 alignment for LOOPNEZ
 135                                 # (0 mod 4 alignment for LBEG)
 136 .Lbyteset:
 137 #if XCHAL_HAVE_LOOPS
 138         loopnez a4, .Lbytesetdone
 139 #else /* !XCHAL_HAVE_LOOPS */
 140         beqz    a4, .Lbytesetdone
 141         add     a6, a5, a4      # a6 = ending address
 142 #endif /* !XCHAL_HAVE_LOOPS */
 143 .Lbyteloop:
 144         EX(s8i, a3, a5, 0, memset_fixup)
 145         addi    a5, a5, 1
 146 #if !XCHAL_HAVE_LOOPS
 147         blt     a5, a6, .Lbyteloop
 148 #endif /* !XCHAL_HAVE_LOOPS */
 149 .Lbytesetdone:
 150         retw
 151
 152
 153         .section .fixup, "ax"
 154         .align  4
 155
 156 /* We return zero if a failure occurred. */
 157
 158 memset_fixup:
 159         movi    a2, 0
 160         retw