From 3712c0af48b9cc68fe52729cb7aa24006e35cb5d Mon Sep 17 00:00:00 2001
From: Alexis Hovorka <alexisspacegirl@gmail.com>
Date: Sat, 17 Aug 2024 19:32:33 -0600
Subject: [post] AArch64 Bootstrapping 1

---
 static/20240817-aarch64-bootstrapping-1/hex.c | 32 +++++++++
 static/20240817-aarch64-bootstrapping-1/hex.s | 95 +++++++++++++++++++++++++++
 2 files changed, 127 insertions(+)
 create mode 100644 static/20240817-aarch64-bootstrapping-1/hex.c
 create mode 100644 static/20240817-aarch64-bootstrapping-1/hex.s

(limited to 'static/20240817-aarch64-bootstrapping-1')

diff --git a/static/20240817-aarch64-bootstrapping-1/hex.c b/static/20240817-aarch64-bootstrapping-1/hex.c
new file mode 100644
index 0000000..aca16e2
--- /dev/null
+++ b/static/20240817-aarch64-bootstrapping-1/hex.c
@@ -0,0 +1,32 @@
+#include <stdio.h>
+
+int main(void) {
+  char c = 0;      // Input character
+  int count = 0;   // Hex digits parsed for this number
+  long long v = 0; // Current value
+
+  while ((c = getchar()) != EOF) {
+
+    // Skip comments
+    if (c == '\\') { while ((c = getchar()) != EOF && c != '\n') {} }
+
+    // Process incoming digits and add to running value
+    else if (('0' <= c) && (c <= '9')) { v = (v << 4) + (c - '0'); count++; }
+    else if (('a' <= c) && (c <= 'f')) { v = (v << 4) + (c - 'a' + 10); count++; }
+
+    // Send the finished number out the other end
+    else if (c == ' ') {
+
+      // Turn the number of hex digits into a number of bytes
+      if (count & 1) count++;
+      count >>= 1;
+
+      // Emit each byte, littlest first
+      for (; count>0; count--) {
+        c = v & 0xFF;
+        putchar(c);
+        v >>= 8;
+      }
+    }
+  }
+}
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
-- 
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