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rom/riscv3/romlib/c_lib/src/machine/riscv/strcmp.S

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+#include <sys/asm.h>
+
+#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 at a time, favoring strings of a couple dozen chars
+#if __riscv_xlen == 32
+  check_one_word 0 5
+  check_one_word 1 5
+  check_one_word 2 5
+  check_one_word 3 5
+  check_one_word 4 5
+#else
+  check_one_word 0 3
+  check_one_word 1 3
+  check_one_word 2 3
+#endif
+  # backwards branch to .Lloop contained above
+
+.Lmismatch:
+  # words don't match, but a2 has no null byte.
+#if __riscv_xlen == 64
+  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
+#if __riscv_xlen == 32
+  foundnull 0 5
+  foundnull 1 5
+  foundnull 2 5
+  foundnull 3 5
+  foundnull 4 5
+#else
+  foundnull 0 3
+  foundnull 1 3
+  foundnull 2 3
+#endif
+
+#if SZREG == 8
+.section .srodata.cst8,"aM",@progbits,8
+.align 3
+mask:
+.dword 0x7f7f7f7f7f7f7f7f
+#endif