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# Artisanally coded in California by A. Shell Waterman

#include 

#if BYTE_ORDER != LITTLE_ENDIAN

# error

#endif

.text

.globl strcmp

strcmp:

  or    a4, a0, a1

  li    t2, -1

  and   a4, a4, SZREG-1

  bnez  a4, .Lmisaligned

#if SZREG == 4

  li t3, 0x7f7f7f7f

#else

  ld t3, mask

#endif

  .macro check_one_word i n

    REG_L a2, \i*SZREG(a0)

    REG_L a3, \i*SZREG(a1)

    and   t0, a2, t3

    or    t1, a2, t3

    add   t0, t0, t3

    or    t0, t0, t1

    bne   t0, t2, .Lnull\i

    .if \i+1-\n

      bne   a2, a3, .Lmismatch

    .else

      add   a0, a0, \n*SZREG

      add   a1, a1, \n*SZREG

      beq   a2, a3, .Lloop

      # fall through to .Lmismatch

    .endif

  .endm

  .macro foundnull i n

    .ifne \i

      .Lnull\i:

      add   a0, a0, \i*SZREG

      add   a1, a1, \i*SZREG

      .ifeq \i-1

        .Lnull0:

      .endif

      bne   a2, a3, .Lmisaligned

      li    a0, 0

      ret

    .endif

  .endm

.Lloop:

  # examine full words

  check_one_word 0 3

  check_one_word 1 3

  check_one_word 2 3

  # backwards branch to .Lloop contained above

.Lmismatch:

  # words don't match, but a2 has no null byte.

#ifdef __riscv64

  sll   a4, a2, 48

  sll   a5, a3, 48

  bne   a4, a5, .Lmismatch_upper

  sll   a4, a2, 32

  sll   a5, a3, 32

  bne   a4, a5, .Lmismatch_upper

#endif

  sll   a4, a2, 16

  sll   a5, a3, 16

  bne   a4, a5, .Lmismatch_upper

  srl   a4, a2, 8*SZREG-16

  srl   a5, a3, 8*SZREG-16

  sub   a0, a4, a5

  and   a1, a0, 0xff

  bnez  a1, 1f

  ret

.Lmismatch_upper:

  srl   a4, a4, 8*SZREG-16

  srl   a5, a5, 8*SZREG-16

  sub   a0, a4, a5

  and   a1, a0, 0xff

  bnez  a1, 1f

  ret

1:and   a4, a4, 0xff

  and   a5, a5, 0xff

  sub   a0, a4, a5

  ret

.Lmisaligned:

  # misaligned

  lbu   a2, 0(a0)

  lbu   a3, 0(a1)

  add   a0, a0, 1

  add   a1, a1, 1

  bne   a2, a3, 1f

  bnez  a2, .Lmisaligned

1:

  sub   a0, a2, a3

  ret

  # cases in which a null byte was detected

  foundnull 0, 3

  foundnull 1, 3

  foundnull 2, 3

#if SZREG == 8

.section .srodata.cst8,"aM",@progbits,8

.align 3

mask:

.dword 0x7f7f7f7f7f7f7f7f

#endif