7842 - new directory organization

Baremetal is now the default build target and therefore has its sources
at the top-level. Baremetal programs build using the phase-2 Mu toolchain
that requires a Linux kernel. This phase-2 codebase which used to be at
the top-level is now under the linux/ directory. Finally, the phase-2 toolchain,
while self-hosting, has a way to bootstrap from a C implementation, which
is now stored in linux/bootstrap. The bootstrap C implementation uses some
literate programming tools that are now in linux/bootstrap/tools.

So the whole thing has gotten inverted. Each directory should build one
artifact and include the main sources (along with standard library). Tools
used for building it are relegated to sub-directories, even though those
tools are often useful in their own right, and have had lots of interesting
programs written using them.

A couple of things have gotten dropped in this process:
  - I had old ways to run on just a Linux kernel, or with a Soso kernel.
    No more.
  - I had some old tooling for running a single test at the cursor. I haven't
    used that lately. Maybe I'll bring it back one day.

The reorg isn't done yet. Still to do:
  - redo documentation everywhere. All the README files, all other markdown,
    particularly vocabulary.md.
  - clean up how-to-run comments at the start of programs everywhere
  - rethink what to do with the html/ directory. Do we even want to keep
    supporting it?

In spite of these shortcomings, all the scripts at the top-level, linux/
and linux/bootstrap are working. The names of the scripts also feel reasonable.
This is a good milestone to take stock at.

1 files changed, 107 insertions, 0 deletions

diff --git a/linux/advent2020/3a.mu b/linux/advent2020/3a.mu
new file mode 100644
index 00000000..76bda961
--- /dev/null
+++ b/linux/advent2020/3a.mu
@@ -0,0 +1,107 @@
+# https://adventofcode.com/2020/day/3
+#
+# To run (on Linux):
+#   $ git clone https://github.com/akkartik/mu
+#   $ cd mu
+#   $ ./translate_mu apps/advent2020/3a.mu
+#   $ ./a.elf < input
+#
+# You'll need to register to download the 'input' file for yourself.
+
+fn main -> _/ebx: int {
+  # represent trees in a 2D array of ints
+  # wasteful since each tree is just one bit
+  var trees-storage: (array int 0x2800)  # 10k ints
+  var trees/esi: (addr array int) <- address trees-storage
+  var trees-length/ecx: int <- copy 0
+  var num-rows: int
+  var width: int
+  # phase 1: parse each row of trees from stdin
+  {
+    var line-storage: (stream byte 0x40)  # 64 bytes
+    var line/edx: (addr stream byte) <- address line-storage
+    {
+      # read line from stdin
+      clear-stream line
+      read-line-from-real-keyboard line
+      # if line is empty (not even a newline), quit
+      var done?/eax: boolean <- stream-empty? line
+      compare done?, 0/false
+      break-if-!=
+      # wastefully recompute width on every line
+      # zero error-checking; we assume input lines are all equally long
+      copy-to width, 0
+      # turn each byte into a tree and append it
+      $main:line-loop: {
+        var done?/eax: boolean <- stream-empty? line
+        compare done?, 0/false
+        break-if-!=
+#?         print-int32-decimal 0, num-rows
+#?         print-string 0, " "
+#?         print-int32-decimal 0, width
+#?         print-string 0, "\n"
+        var dest/ebx: (addr int) <- index trees, trees-length
+        var c/eax: byte <- read-byte line
+        # newline comes only at end of line
+        compare c, 0xa/newline
+        break-if-=
+        # '#' = tree
+        compare c, 0x23/hash
+        {
+          break-if-!=
+          copy-to *dest, 1
+        }
+        # anything else = no tree
+        {
+          break-if-=
+          copy-to *dest, 0
+        }
+        increment width
+        trees-length <- increment
+        loop
+      }
+      increment num-rows
+      loop
+    }
+  }
+  # phase 2: compute
+  print-int32-decimal 0, num-rows
+  print-string 0, "x"
+  print-int32-decimal 0, width
+  print-string 0, "\n"
+  var row/ecx: int <- copy 0
+  var col/edx: int <- copy 0
+  var num-trees-hit/edi: int <- copy 0
+  {
+    compare row, num-rows
+    break-if->=
+    var curr/eax: int <- index2d trees, row, col, width
+    compare curr, 0
+    {
+      break-if-=
+      num-trees-hit <- increment
+    }
+    # right 3, down 1
+    col <- add 3
+    row <- add 1
+    loop
+  }
+  print-int32-decimal 0, num-trees-hit
+  print-string 0, "\n"
+  return 0
+}
+
+fn index2d _arr: (addr array int), _row: int, _col: int, width: int -> _/eax: int {
+  # handle repeating columns of trees
+  var dummy/eax: int <- copy 0
+  var col/edx: int <- copy 0
+  dummy, col <- integer-divide _col, width
+  # compute index
+  var index/eax: int <- copy _row
+  index <- multiply width
+  index <- add col
+  # look up array
+  var arr/esi: (addr array int) <- copy _arr
+  var src/eax: (addr int) <- index arr, index
+  return *src
+}