From 2133d8675e828cca541b46ff0a51a8885f853def Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Mon, 4 Mar 2019 17:23:53 +0100
Subject: mg2d: refactor levels allocation

This should simplify future improvements.
---
 mg2d.c | 69 ++++++++++++++++++++++++++++++++----------------------------------
 1 file changed, 33 insertions(+), 36 deletions(-)

diff --git a/mg2d.c b/mg2d.c
index eb3973b..5f5b73e 100644
--- a/mg2d.c
+++ b/mg2d.c
@@ -622,45 +622,42 @@ static int log2i(int n)
 static int mg_levels_alloc(MG2DContext *ctx, size_t domain_size)
 {
     MG2DInternal *priv = ctx->priv;
-    MG2DLevel *cur, **last;
-    size_t last_size;
-    unsigned int last_depth;
-
-    priv->root = mg_level_alloc(EGS_SOLVER_RELAXATION, domain_size);
-    if (!priv->root)
-        return -ENOMEM;
-
-    // choose the domain size for the first child
-    // the children all have sizes 2**n + 1
-    // but we skip the closest lower one if it is too close
-    if (domain_size <= 2)
-        goto finish;
-    domain_size = (1 << log2i(domain_size - 2)) + 1;
-    if ((double)priv->root->solver->domain_size[0] / domain_size  < 1.5)
-        domain_size = (domain_size >> 1) + 1;
-
-    cur = priv->root;
-    for (int i = 0; i < LEVELS_MAX && domain_size > 4; i++) {
-        cur->child = mg_level_alloc(EGS_SOLVER_RELAXATION, domain_size);
-        if (!cur->child)
+
+    MG2DLevel **dst;
+    enum EGSType next_type;
+    size_t next_size;
+
+    dst       = &priv->root;
+    next_size = domain_size;
+
+    for (int depth = 0; depth < LEVELS_MAX; depth++) {
+        enum EGSType cur_type;
+        size_t cur_size = next_size;
+
+        // choose the domain size for the next child
+        // the children all have sizes 2**n + 1
+        // but on the top level we skip the closest lower one if it is too close
+        if (depth == 0) {
+            next_size = (1 << log2i(cur_size - 2)) + 1;
+            if ((double)cur_size / next_size  < 1.5)
+                next_size = (next_size >> 1) + 1;
+        } else
+            next_size = (cur_size >> 1) + 1;
+
+        cur_type = (depth == LEVELS_MAX - 1 || cur_size < 9) ? EGS_SOLVER_EXACT : EGS_SOLVER_RELAXATION;
+
+        *dst = mg_level_alloc(cur_type, cur_size);
+        if (!*dst)
             return -ENOMEM;
-        cur->child->depth = i + 1;
+        (*dst)->depth = depth;
 
-        cur = cur->child;
-        domain_size = (domain_size >> 1) + 1;
-    }
+        if (cur_type == EGS_SOLVER_EXACT)
+            break;
+        if (next_size <= 4)
+            break;
 
-finish:
-    last = &priv->root;
-    while ((*last)->child)
-        last = &((*last)->child);
-    last_size = (*last)->solver->domain_size[0];
-    last_depth = (*last)->depth;
-    mg_level_free(last);
-    *last = mg_level_alloc(EGS_SOLVER_EXACT, last_size);
-    if (!*last)
-        return -ENOMEM;
-    (*last)->depth = last_depth;
+        dst = &(*dst)->child;
+    }
 
     return 0;
 }
-- 
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