Deps log format v3

This fixes two bugs.

1.) It makes the record size field 4 byte instead of 2, and allows a max
    record size of 512kB. This fixes #605, ninja "only" supporting 8k
    dependencies per file -- 512kB have room for 128k dependencies. (If that's
    still not enough, the current design can support at least 4x that if the
    constant is tweaked.)

2.) It makes all records 4-byte aligned, which is probably needed to make the
    `reinterpret_cast<int*>(buf)` work on SPARC (cf issue #481), and it's
    generally nicer too. (Since there's already one reinterpret_cast, convert
    a memcpy() to reinterpret_cast in another branch too).

1 files changed, 4 insertions, 3 deletions

diff --git a/src/deps_log.h b/src/deps_log.h
index 47ade03..babf828 100644
--- a/src/deps_log.h
+++ b/src/deps_log.h
@@ -50,9 +50,10 @@ struct State;
 /// A dependency list maps an output id to a list of input ids.
 ///
 /// Concretely, a record is:
-///    two bytes record length, high bit indicates record type
-///      (implies max record length 32k)
-///    path records contain the string name of the path, followed by the
+///    four bytes record length, high bit indicates record type
+///      (but max record sizes are capped at 512kB)
+///    path records contain the string name of the path, followed by up to 3
+///      padding bytes to align on 4 byte boundaries, followed by the
 ///      one's complement of the expected index of the record (to detect
 ///      concurrent writes of multiple ninja processes to the log).
 ///    dependency records are an array of 4-byte integers