[post] AArch64 Bootstrapping 1

1 files changed, 95 insertions, 0 deletions

diff --git a/static/20240817-aarch64-bootstrapping-1/hex.s b/static/20240817-aarch64-bootstrapping-1/hex.s
new file mode 100644
index 0000000..b120014
--- /dev/null
+++ b/static/20240817-aarch64-bootstrapping-1/hex.s
@@ -0,0 +1,95 @@
+.section .data
+buf:
+  .byte 0       // input/output character buffer
+
+.section .text
+.global _start
+_start:
+  mov x19, #0   // value
+  mov x20, #0   // count
+
+loop:
+  mov x8, #63   // read
+  mov x0, #0    // stdin
+  adr x1, buf
+  mov x2, #1
+  svc 0
+
+  cmp x0, #0    // count of bytes read; 0 means EOF
+  b.ne 1f
+
+exit:
+  mov x8, #93   // exit
+  mov x0, #0    // error code (no error)
+  svc 0
+
+1:
+  adr x1, buf
+  ldurb w9, [x1]
+
+  cmp w9, #92   // backslash; start of comment
+  b.ne 2f
+
+comment:
+  mov x8, #63   // read
+  mov x0, #0    // stdin
+  adr x1, buf
+  mov x2, #1
+  svc 0
+
+  cmp x0, #0
+  b.eq exit
+
+  adr x1, buf
+  ldurb w9, [x1]
+  cmp w9, '\n'
+  b.ne comment
+  b loop
+
+2:
+  cmp w9, '0'
+  b.lt 3f
+  cmp w9, '9'
+  b.gt 3f
+
+  sub w9, w9, '0'
+  b 4f
+
+3:
+  cmp w9, 'a'
+  b.lt 5f
+  cmp w9, 'f'
+  b.gt 5f
+
+  sub w9, w9, ('a' - 10)
+  b 4f
+
+4:
+  lsl x19, x19, #4
+  add x19, x19, w9, uxtb
+  add x20, x20, #1
+  b loop
+
+5:
+  cmp w9, ' '
+  b.ne loop
+
+  tst x20, #1
+  cinc x20, x20, ne
+  lsr x20, x20, #1
+
+6:
+  cmp x20, #0
+  b.eq loop
+
+  mov x8, #64   // write
+  mov x0, #1    // stdout
+  adr x1, buf
+  sturb w19, [x1]
+  mov x2, #1
+  svc 0
+
+  lsr x19, x19, #8
+
+  sub x20, x20, #1
+  b 6b