document the algorithm a bit

[r26713]

diff --git a/ir/be/beemitter_binary.c b/ir/be/beemitter_binary.c
index 5765078..e9291e6 100644 (file)
--- a/ir/be/beemitter_binary.c
+++ b/ir/be/beemitter_binary.c
@@ -121,7 +121,8 @@ static unsigned align(unsigned offset, unsigned alignment)
        return offset;
 }
 
-static bool determine_jumpsize_pass(const binary_emiter_interface_t *interface)
+static bool determine_jumpsize_iteration(
+               const binary_emiter_interface_t *interface)
 {
        unsigned         offset     = 0;
        unsigned         max_offset = 0;
@@ -137,7 +138,7 @@ static bool determine_jumpsize_pass(const binary_emiter_interface_t *interface)
            max_offset = align(max_offset, alignment);
 
                if (offset != fragment->offset) {
-                       changed = true;
+                       changed          = true;
                        fragment->offset = offset;
                }
            fragment->max_offset = max_offset;
@@ -161,9 +162,14 @@ static void determine_offsets(const binary_emiter_interface_t *interface)
        first_fragment->offset     = 0;
        first_fragment->max_offset = 0;
 
-       /* pass1: encode minimum/maximum offsets into fragments */
+       /* The algorithm calculates a lower and upper bound for the offset of each
+        * fragment. With this information we can calculate a lower and upper bound
+        * for the size of each jump instruction.
+        * A single iteration updates the offset bounds for all fragments and jump
+        * sizes for each fragment. We iterate until we had an iteration where
+        * none of the minimum offsets changed. */
        do {
-               changed = determine_jumpsize_pass(interface);
+               changed = determine_jumpsize_iteration(interface);
                /* TODO: we should have an abort mode for the case when the offsets
                   don't converge fast enough. We could simply use a pessimistic
                   solution after a few iterations... */