From 6e1eeeebfb453fa7c871869c19375ce60fbd7413 Mon Sep 17 00:00:00 2001
From: Kartik Agaram <vc@akkartik.com>
Date: Sat, 27 Jul 2019 16:01:55 -0700
Subject: 5485 - promote SubX to top-level

---
 examples/ex9.subx | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 examples/ex9.subx

(limited to 'examples/ex9.subx')

diff --git a/examples/ex9.subx b/examples/ex9.subx
new file mode 100644
index 00000000..e3318b05
--- /dev/null
+++ b/examples/ex9.subx
@@ -0,0 +1,55 @@
+# Example showing arg order on the stack.
+#
+# Show difference between ascii codes of first letter of first arg and first
+# letter of second arg.
+#
+# To run (from the subx directory):
+#   $ ./subx translate examples/ex9.subx -o examples/ex9
+#   $ ./subx run examples/ex9 z x
+# Expected result:
+#   $ echo $?
+#   2
+#
+# At the start of a SubX program:
+#   argc: *ESP
+#   argv[0]: *(ESP+4)
+#   argv[1]: *(ESP+8)
+#   ...
+# Locals start from ESP-4 downwards.
+
+== code 0x09000000
+#   instruction                     effective address                                                   register    displacement    immediate
+# . op          subop               mod             rm32          base        index         scale       r32
+# . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes
+
+Entry:
+    # . prolog
+    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
+    # ascii-difference(argv[1], argv[2])
+    # . . push argv[2]
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
+    # . . push argv[1]
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
+    # . . call
+    e8/call  ascii-difference/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # syscall(exit, EAX)
+    89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
+    b8/copy-to-EAX  1/imm32/exit
+    cd/syscall  0x80/imm8
+
+ascii-difference:  # (s1, s2) : null-terminated ascii strings
+    # a = first letter of s1 (ECX)
+    8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              0/r32/EAX   4/disp8         .                 # copy *(ESP+4) to EAX
+    8b/copy                         0/mod/indirect  0/rm32/EAX    .           .             .           0/r32/EAX   .               .                 # copy *EAX to EAX
+    # b = first letter of s2 (EDX)
+    8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              1/r32/ECX   8/disp8                           # copy *(ESP+8) to ECX
+    8b/copy                         0/mod/indirect  1/rm32/ECX    .           .             .           1/r32/ECX   .               .                 # copy *ECX to ECX
+    # a-b
+    29/subtract                     3/mod/direct    0/rm32/EAX    .           .             .           1/r32/ECX   .               .                 # subtract ECX from EAX
+    c3/return
+
+== data 0x0a000000
+
+# . . vim:nowrap:textwidth=0
-- 
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