linux/arch/sparc/lib/checksum_32.S
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   1/* SPDX-License-Identifier: GPL-2.0 */
   2/* checksum.S: Sparc optimized checksum code.
   3 *
   4 *  Copyright(C) 1995 Linus Torvalds
   5 *  Copyright(C) 1995 Miguel de Icaza
   6 *  Copyright(C) 1996 David S. Miller
   7 *  Copyright(C) 1997 Jakub Jelinek
   8 *
   9 * derived from:
  10 *      Linux/Alpha checksum c-code
  11 *      Linux/ix86 inline checksum assembly
  12 *      RFC1071 Computing the Internet Checksum (esp. Jacobsons m68k code)
  13 *      David Mosberger-Tang for optimized reference c-code
  14 *      BSD4.4 portable checksum routine
  15 */
  16
  17#include <asm/errno.h>
  18#include <asm/export.h>
  19
  20#define CSUM_BIGCHUNK(buf, offset, sum, t0, t1, t2, t3, t4, t5) \
  21        ldd     [buf + offset + 0x00], t0;                      \
  22        ldd     [buf + offset + 0x08], t2;                      \
  23        addxcc  t0, sum, sum;                                   \
  24        addxcc  t1, sum, sum;                                   \
  25        ldd     [buf + offset + 0x10], t4;                      \
  26        addxcc  t2, sum, sum;                                   \
  27        addxcc  t3, sum, sum;                                   \
  28        ldd     [buf + offset + 0x18], t0;                      \
  29        addxcc  t4, sum, sum;                                   \
  30        addxcc  t5, sum, sum;                                   \
  31        addxcc  t0, sum, sum;                                   \
  32        addxcc  t1, sum, sum;
  33
  34#define CSUM_LASTCHUNK(buf, offset, sum, t0, t1, t2, t3)        \
  35        ldd     [buf - offset - 0x08], t0;                      \
  36        ldd     [buf - offset - 0x00], t2;                      \
  37        addxcc  t0, sum, sum;                                   \
  38        addxcc  t1, sum, sum;                                   \
  39        addxcc  t2, sum, sum;                                   \
  40        addxcc  t3, sum, sum;
  41
  42        /* Do end cruft out of band to get better cache patterns. */
  43csum_partial_end_cruft:
  44        be      1f                              ! caller asks %o1 & 0x8
  45         andcc  %o1, 4, %g0                     ! nope, check for word remaining
  46        ldd     [%o0], %g2                      ! load two
  47        addcc   %g2, %o2, %o2                   ! add first word to sum
  48        addxcc  %g3, %o2, %o2                   ! add second word as well
  49        add     %o0, 8, %o0                     ! advance buf ptr
  50        addx    %g0, %o2, %o2                   ! add in final carry
  51        andcc   %o1, 4, %g0                     ! check again for word remaining
  521:      be      1f                              ! nope, skip this code
  53         andcc  %o1, 3, %o1                     ! check for trailing bytes
  54        ld      [%o0], %g2                      ! load it
  55        addcc   %g2, %o2, %o2                   ! add to sum
  56        add     %o0, 4, %o0                     ! advance buf ptr
  57        addx    %g0, %o2, %o2                   ! add in final carry
  58        andcc   %o1, 3, %g0                     ! check again for trailing bytes
  591:      be      1f                              ! no trailing bytes, return
  60         addcc  %o1, -1, %g0                    ! only one byte remains?
  61        bne     2f                              ! at least two bytes more
  62         subcc  %o1, 2, %o1                     ! only two bytes more?
  63        b       4f                              ! only one byte remains
  64         or     %g0, %g0, %o4                   ! clear fake hword value
  652:      lduh    [%o0], %o4                      ! get hword
  66        be      6f                              ! jmp if only hword remains
  67         add    %o0, 2, %o0                     ! advance buf ptr either way
  68        sll     %o4, 16, %o4                    ! create upper hword
  694:      ldub    [%o0], %o5                      ! get final byte
  70        sll     %o5, 8, %o5                     ! put into place
  71        or      %o5, %o4, %o4                   ! coalese with hword (if any)
  726:      addcc   %o4, %o2, %o2                   ! add to sum
  731:      retl                                    ! get outta here
  74         addx   %g0, %o2, %o0                   ! add final carry into retval
  75
  76        /* Also do alignment out of band to get better cache patterns. */
  77csum_partial_fix_alignment:
  78        cmp     %o1, 6
  79        bl      cpte - 0x4
  80         andcc  %o0, 0x2, %g0
  81        be      1f
  82         andcc  %o0, 0x4, %g0
  83        lduh    [%o0 + 0x00], %g2
  84        sub     %o1, 2, %o1
  85        add     %o0, 2, %o0
  86        sll     %g2, 16, %g2
  87        addcc   %g2, %o2, %o2
  88        srl     %o2, 16, %g3
  89        addx    %g0, %g3, %g2
  90        sll     %o2, 16, %o2
  91        sll     %g2, 16, %g3
  92        srl     %o2, 16, %o2
  93        andcc   %o0, 0x4, %g0
  94        or      %g3, %o2, %o2
  951:      be      cpa
  96         andcc  %o1, 0xffffff80, %o3
  97        ld      [%o0 + 0x00], %g2
  98        sub     %o1, 4, %o1
  99        addcc   %g2, %o2, %o2
 100        add     %o0, 4, %o0
 101        addx    %g0, %o2, %o2
 102        b       cpa
 103         andcc  %o1, 0xffffff80, %o3
 104
 105        /* The common case is to get called with a nicely aligned
 106         * buffer of size 0x20.  Follow the code path for that case.
 107         */
 108        .globl  csum_partial
 109        EXPORT_SYMBOL(csum_partial)
 110csum_partial:                   /* %o0=buf, %o1=len, %o2=sum */
 111        andcc   %o0, 0x7, %g0                           ! alignment problems?
 112        bne     csum_partial_fix_alignment              ! yep, handle it
 113         sethi  %hi(cpte - 8), %g7                      ! prepare table jmp ptr
 114        andcc   %o1, 0xffffff80, %o3                    ! num loop iterations
 115cpa:    be      3f                                      ! none to do
 116         andcc  %o1, 0x70, %g1                          ! clears carry flag too
 1175:      CSUM_BIGCHUNK(%o0, 0x00, %o2, %o4, %o5, %g2, %g3, %g4, %g5)
 118        CSUM_BIGCHUNK(%o0, 0x20, %o2, %o4, %o5, %g2, %g3, %g4, %g5)
 119        CSUM_BIGCHUNK(%o0, 0x40, %o2, %o4, %o5, %g2, %g3, %g4, %g5)
 120        CSUM_BIGCHUNK(%o0, 0x60, %o2, %o4, %o5, %g2, %g3, %g4, %g5)
 121        addx    %g0, %o2, %o2                           ! sink in final carry
 122        subcc   %o3, 128, %o3                           ! detract from loop iters
 123        bne     5b                                      ! more to do
 124         add    %o0, 128, %o0                           ! advance buf ptr
 125        andcc   %o1, 0x70, %g1                          ! clears carry flag too
 1263:      be      cpte                                    ! nope
 127         andcc  %o1, 0xf, %g0                           ! anything left at all?
 128        srl     %g1, 1, %o4                             ! compute offset
 129        sub     %g7, %g1, %g7                           ! adjust jmp ptr
 130        sub     %g7, %o4, %g7                           ! final jmp ptr adjust
 131        jmp     %g7 + %lo(cpte - 8)                     ! enter the table
 132         add    %o0, %g1, %o0                           ! advance buf ptr
 133cptbl:  CSUM_LASTCHUNK(%o0, 0x68, %o2, %g2, %g3, %g4, %g5)
 134        CSUM_LASTCHUNK(%o0, 0x58, %o2, %g2, %g3, %g4, %g5)
 135        CSUM_LASTCHUNK(%o0, 0x48, %o2, %g2, %g3, %g4, %g5)
 136        CSUM_LASTCHUNK(%o0, 0x38, %o2, %g2, %g3, %g4, %g5)
 137        CSUM_LASTCHUNK(%o0, 0x28, %o2, %g2, %g3, %g4, %g5)
 138        CSUM_LASTCHUNK(%o0, 0x18, %o2, %g2, %g3, %g4, %g5)
 139        CSUM_LASTCHUNK(%o0, 0x08, %o2, %g2, %g3, %g4, %g5)
 140        addx    %g0, %o2, %o2                           ! fetch final carry
 141        andcc   %o1, 0xf, %g0                           ! anything left at all?
 142cpte:   bne     csum_partial_end_cruft                  ! yep, handle it
 143         andcc  %o1, 8, %g0                             ! check how much
 144cpout:  retl                                            ! get outta here
 145         mov    %o2, %o0                                ! return computed csum
 146
 147/* Work around cpp -rob */
 148#define ALLOC #alloc
 149#define EXECINSTR #execinstr
 150#define EX(x,y)                                 \
 15198:     x,y;                                    \
 152        .section __ex_table,ALLOC;              \
 153        .align  4;                              \
 154        .word   98b, cc_fault;                   \
 155        .text;                                  \
 156        .align  4
 157
 158        /* This aligned version executes typically in 8.5 superscalar cycles, this
 159         * is the best I can do.  I say 8.5 because the final add will pair with
 160         * the next ldd in the main unrolled loop.  Thus the pipe is always full.
 161         * If you change these macros (including order of instructions),
 162         * please check the fixup code below as well.
 163         */
 164#define CSUMCOPY_BIGCHUNK_ALIGNED(src, dst, sum, off, t0, t1, t2, t3, t4, t5, t6, t7)   \
 165        EX(ldd  [src + off + 0x00], t0);                                                \
 166        EX(ldd  [src + off + 0x08], t2);                                                \
 167        addxcc  t0, sum, sum;                                                           \
 168        EX(ldd  [src + off + 0x10], t4);                                                \
 169        addxcc  t1, sum, sum;                                                           \
 170        EX(ldd  [src + off + 0x18], t6);                                                \
 171        addxcc  t2, sum, sum;                                                           \
 172        EX(std  t0, [dst + off + 0x00]);                                                \
 173        addxcc  t3, sum, sum;                                                           \
 174        EX(std  t2, [dst + off + 0x08]);                                                \
 175        addxcc  t4, sum, sum;                                                           \
 176        EX(std  t4, [dst + off + 0x10]);                                                \
 177        addxcc  t5, sum, sum;                                                           \
 178        EX(std  t6, [dst + off + 0x18]);                                                \
 179        addxcc  t6, sum, sum;                                                           \
 180        addxcc  t7, sum, sum;
 181
 182        /* 12 superscalar cycles seems to be the limit for this case,
 183         * because of this we thus do all the ldd's together to get
 184         * Viking MXCC into streaming mode.  Ho hum...
 185         */
 186#define CSUMCOPY_BIGCHUNK(src, dst, sum, off, t0, t1, t2, t3, t4, t5, t6, t7)   \
 187        EX(ldd  [src + off + 0x00], t0);                                        \
 188        EX(ldd  [src + off + 0x08], t2);                                        \
 189        EX(ldd  [src + off + 0x10], t4);                                        \
 190        EX(ldd  [src + off + 0x18], t6);                                        \
 191        EX(st   t0, [dst + off + 0x00]);                                        \
 192        addxcc  t0, sum, sum;                                                   \
 193        EX(st   t1, [dst + off + 0x04]);                                        \
 194        addxcc  t1, sum, sum;                                                   \
 195        EX(st   t2, [dst + off + 0x08]);                                        \
 196        addxcc  t2, sum, sum;                                                   \
 197        EX(st   t3, [dst + off + 0x0c]);                                        \
 198        addxcc  t3, sum, sum;                                                   \
 199        EX(st   t4, [dst + off + 0x10]);                                        \
 200        addxcc  t4, sum, sum;                                                   \
 201        EX(st   t5, [dst + off + 0x14]);                                        \
 202        addxcc  t5, sum, sum;                                                   \
 203        EX(st   t6, [dst + off + 0x18]);                                        \
 204        addxcc  t6, sum, sum;                                                   \
 205        EX(st   t7, [dst + off + 0x1c]);                                        \
 206        addxcc  t7, sum, sum;
 207
 208        /* Yuck, 6 superscalar cycles... */
 209#define CSUMCOPY_LASTCHUNK(src, dst, sum, off, t0, t1, t2, t3)  \
 210        EX(ldd  [src - off - 0x08], t0);                        \
 211        EX(ldd  [src - off - 0x00], t2);                        \
 212        addxcc  t0, sum, sum;                                   \
 213        EX(st   t0, [dst - off - 0x08]);                        \
 214        addxcc  t1, sum, sum;                                   \
 215        EX(st   t1, [dst - off - 0x04]);                        \
 216        addxcc  t2, sum, sum;                                   \
 217        EX(st   t2, [dst - off - 0x00]);                        \
 218        addxcc  t3, sum, sum;                                   \
 219        EX(st   t3, [dst - off + 0x04]);
 220
 221        /* Handle the end cruft code out of band for better cache patterns. */
 222cc_end_cruft:
 223        be      1f
 224         andcc  %o3, 4, %g0
 225        EX(ldd  [%o0 + 0x00], %g2)
 226        add     %o1, 8, %o1
 227        addcc   %g2, %g7, %g7
 228        add     %o0, 8, %o0
 229        addxcc  %g3, %g7, %g7
 230        EX(st   %g2, [%o1 - 0x08])
 231        addx    %g0, %g7, %g7
 232        andcc   %o3, 4, %g0
 233        EX(st   %g3, [%o1 - 0x04])
 2341:      be      1f
 235         andcc  %o3, 3, %o3
 236        EX(ld   [%o0 + 0x00], %g2)
 237        add     %o1, 4, %o1
 238        addcc   %g2, %g7, %g7
 239        EX(st   %g2, [%o1 - 0x04])
 240        addx    %g0, %g7, %g7
 241        andcc   %o3, 3, %g0
 242        add     %o0, 4, %o0
 2431:      be      1f
 244         addcc  %o3, -1, %g0
 245        bne     2f
 246         subcc  %o3, 2, %o3
 247        b       4f
 248         or     %g0, %g0, %o4
 2492:      EX(lduh [%o0 + 0x00], %o4)
 250        add     %o0, 2, %o0
 251        EX(sth  %o4, [%o1 + 0x00])
 252        be      6f
 253         add    %o1, 2, %o1
 254        sll     %o4, 16, %o4
 2554:      EX(ldub [%o0 + 0x00], %o5)
 256        EX(stb  %o5, [%o1 + 0x00])
 257        sll     %o5, 8, %o5
 258        or      %o5, %o4, %o4
 2596:      addcc   %o4, %g7, %g7
 2601:      retl
 261         addx   %g0, %g7, %o0
 262
 263        /* Also, handle the alignment code out of band. */
 264cc_dword_align:
 265        cmp     %g1, 16
 266        bge     1f
 267         srl    %g1, 1, %o3
 2682:      cmp     %o3, 0
 269        be,a    ccte
 270         andcc  %g1, 0xf, %o3
 271        andcc   %o3, %o0, %g0   ! Check %o0 only (%o1 has the same last 2 bits)
 272        be,a    2b
 273         srl    %o3, 1, %o3
 2741:      andcc   %o0, 0x1, %g0
 275        bne     ccslow
 276         andcc  %o0, 0x2, %g0
 277        be      1f
 278         andcc  %o0, 0x4, %g0
 279        EX(lduh [%o0 + 0x00], %g4)
 280        sub     %g1, 2, %g1
 281        EX(sth  %g4, [%o1 + 0x00])
 282        add     %o0, 2, %o0
 283        sll     %g4, 16, %g4
 284        addcc   %g4, %g7, %g7
 285        add     %o1, 2, %o1
 286        srl     %g7, 16, %g3
 287        addx    %g0, %g3, %g4
 288        sll     %g7, 16, %g7
 289        sll     %g4, 16, %g3
 290        srl     %g7, 16, %g7
 291        andcc   %o0, 0x4, %g0
 292        or      %g3, %g7, %g7
 2931:      be      3f
 294         andcc  %g1, 0xffffff80, %g0
 295        EX(ld   [%o0 + 0x00], %g4)
 296        sub     %g1, 4, %g1
 297        EX(st   %g4, [%o1 + 0x00])
 298        add     %o0, 4, %o0
 299        addcc   %g4, %g7, %g7
 300        add     %o1, 4, %o1
 301        addx    %g0, %g7, %g7
 302        b       3f
 303         andcc  %g1, 0xffffff80, %g0
 304
 305        /* Sun, you just can't beat me, you just can't.  Stop trying,
 306         * give up.  I'm serious, I am going to kick the living shit
 307         * out of you, game over, lights out.
 308         */
 309        .align  8
 310        .globl  __csum_partial_copy_sparc_generic
 311        EXPORT_SYMBOL(__csum_partial_copy_sparc_generic)
 312__csum_partial_copy_sparc_generic:
 313                                        /* %o0=src, %o1=dest, %g1=len, %g7=sum */
 314        xor     %o0, %o1, %o4           ! get changing bits
 315        andcc   %o4, 3, %g0             ! check for mismatched alignment
 316        bne     ccslow                  ! better this than unaligned/fixups
 317         andcc  %o0, 7, %g0             ! need to align things?
 318        bne     cc_dword_align          ! yes, we check for short lengths there
 319         andcc  %g1, 0xffffff80, %g0    ! can we use unrolled loop?
 3203:      be      3f                      ! nope, less than one loop remains
 321         andcc  %o1, 4, %g0             ! dest aligned on 4 or 8 byte boundary?
 322        be      ccdbl + 4               ! 8 byte aligned, kick ass
 3235:      CSUMCOPY_BIGCHUNK(%o0,%o1,%g7,0x00,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 324        CSUMCOPY_BIGCHUNK(%o0,%o1,%g7,0x20,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 325        CSUMCOPY_BIGCHUNK(%o0,%o1,%g7,0x40,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 326        CSUMCOPY_BIGCHUNK(%o0,%o1,%g7,0x60,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 327        sub     %g1, 128, %g1           ! detract from length
 328        addx    %g0, %g7, %g7           ! add in last carry bit
 329        andcc   %g1, 0xffffff80, %g0    ! more to csum?
 330        add     %o0, 128, %o0           ! advance src ptr
 331        bne     5b                      ! we did not go negative, continue looping
 332         add    %o1, 128, %o1           ! advance dest ptr
 3333:      andcc   %g1, 0x70, %o2          ! can use table?
 334ccmerge:be      ccte                    ! nope, go and check for end cruft
 335         andcc  %g1, 0xf, %o3           ! get low bits of length (clears carry btw)
 336        srl     %o2, 1, %o4             ! begin negative offset computation
 337        sethi   %hi(12f), %o5           ! set up table ptr end
 338        add     %o0, %o2, %o0           ! advance src ptr
 339        sub     %o5, %o4, %o5           ! continue table calculation
 340        sll     %o2, 1, %g2             ! constant multiplies are fun...
 341        sub     %o5, %g2, %o5           ! some more adjustments
 342        jmp     %o5 + %lo(12f)          ! jump into it, duff style, wheee...
 343         add    %o1, %o2, %o1           ! advance dest ptr (carry is clear btw)
 344cctbl:  CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x68,%g2,%g3,%g4,%g5)
 345        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x58,%g2,%g3,%g4,%g5)
 346        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x48,%g2,%g3,%g4,%g5)
 347        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x38,%g2,%g3,%g4,%g5)
 348        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x28,%g2,%g3,%g4,%g5)
 349        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x18,%g2,%g3,%g4,%g5)
 350        CSUMCOPY_LASTCHUNK(%o0,%o1,%g7,0x08,%g2,%g3,%g4,%g5)
 35112:     addx    %g0, %g7, %g7
 352        andcc   %o3, 0xf, %g0           ! check for low bits set
 353ccte:   bne     cc_end_cruft            ! something left, handle it out of band
 354         andcc  %o3, 8, %g0             ! begin checks for that code
 355        retl                            ! return
 356         mov    %g7, %o0                ! give em the computed checksum
 357ccdbl:  CSUMCOPY_BIGCHUNK_ALIGNED(%o0,%o1,%g7,0x00,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 358        CSUMCOPY_BIGCHUNK_ALIGNED(%o0,%o1,%g7,0x20,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 359        CSUMCOPY_BIGCHUNK_ALIGNED(%o0,%o1,%g7,0x40,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 360        CSUMCOPY_BIGCHUNK_ALIGNED(%o0,%o1,%g7,0x60,%o4,%o5,%g2,%g3,%g4,%g5,%o2,%o3)
 361        sub     %g1, 128, %g1           ! detract from length
 362        addx    %g0, %g7, %g7           ! add in last carry bit
 363        andcc   %g1, 0xffffff80, %g0    ! more to csum?
 364        add     %o0, 128, %o0           ! advance src ptr
 365        bne     ccdbl                   ! we did not go negative, continue looping
 366         add    %o1, 128, %o1           ! advance dest ptr
 367        b       ccmerge                 ! finish it off, above
 368         andcc  %g1, 0x70, %o2          ! can use table? (clears carry btw)
 369
 370ccslow: cmp     %g1, 0
 371        mov     0, %g5
 372        bleu    4f
 373         andcc  %o0, 1, %o5             
 374        be,a    1f
 375         srl    %g1, 1, %g4             
 376        sub     %g1, 1, %g1     
 377        EX(ldub [%o0], %g5)
 378        add     %o0, 1, %o0     
 379        EX(stb  %g5, [%o1])
 380        srl     %g1, 1, %g4
 381        add     %o1, 1, %o1
 3821:      cmp     %g4, 0          
 383        be,a    3f
 384         andcc  %g1, 1, %g0
 385        andcc   %o0, 2, %g0     
 386        be,a    1f
 387         srl    %g4, 1, %g4
 388        EX(lduh [%o0], %o4)
 389        sub     %g1, 2, %g1     
 390        srl     %o4, 8, %g2
 391        sub     %g4, 1, %g4     
 392        EX(stb  %g2, [%o1])
 393        add     %o4, %g5, %g5
 394        EX(stb  %o4, [%o1 + 1])
 395        add     %o0, 2, %o0     
 396        srl     %g4, 1, %g4
 397        add     %o1, 2, %o1
 3981:      cmp     %g4, 0          
 399        be,a    2f
 400         andcc  %g1, 2, %g0
 401        EX(ld   [%o0], %o4)
 4025:      srl     %o4, 24, %g2
 403        srl     %o4, 16, %g3
 404        EX(stb  %g2, [%o1])
 405        srl     %o4, 8, %g2
 406        EX(stb  %g3, [%o1 + 1])
 407        add     %o0, 4, %o0
 408        EX(stb  %g2, [%o1 + 2])
 409        addcc   %o4, %g5, %g5
 410        EX(stb  %o4, [%o1 + 3])
 411        addx    %g5, %g0, %g5   ! I am now to lazy to optimize this (question it
 412        add     %o1, 4, %o1     ! is worthy). Maybe some day - with the sll/srl
 413        subcc   %g4, 1, %g4     ! tricks
 414        bne,a   5b
 415         EX(ld  [%o0], %o4)
 416        sll     %g5, 16, %g2
 417        srl     %g5, 16, %g5
 418        srl     %g2, 16, %g2
 419        andcc   %g1, 2, %g0
 420        add     %g2, %g5, %g5 
 4212:      be,a    3f              
 422         andcc  %g1, 1, %g0
 423        EX(lduh [%o0], %o4)
 424        andcc   %g1, 1, %g0
 425        srl     %o4, 8, %g2
 426        add     %o0, 2, %o0     
 427        EX(stb  %g2, [%o1])
 428        add     %g5, %o4, %g5
 429        EX(stb  %o4, [%o1 + 1])
 430        add     %o1, 2, %o1
 4313:      be,a    1f              
 432         sll    %g5, 16, %o4
 433        EX(ldub [%o0], %g2)
 434        sll     %g2, 8, %o4     
 435        EX(stb  %g2, [%o1])
 436        add     %g5, %o4, %g5
 437        sll     %g5, 16, %o4
 4381:      addcc   %o4, %g5, %g5
 439        srl     %g5, 16, %o4
 440        addx    %g0, %o4, %g5
 441        orcc    %o5, %g0, %g0
 442        be      4f
 443         srl    %g5, 8, %o4
 444        and     %g5, 0xff, %g2
 445        and     %o4, 0xff, %o4
 446        sll     %g2, 8, %g2
 447        or      %g2, %o4, %g5
 4484:      addcc   %g7, %g5, %g7
 449        retl    
 450         addx   %g0, %g7, %o0
 451
 452/* We do these strange calculations for the csum_*_from_user case only, ie.
 453 * we only bother with faults on loads... */
 454
 455cc_fault:
 456        ret
 457         clr    %o0
 458