From 21962c91316958d87b8ceba74d89588fc6c974c8 Mon Sep 17 00:00:00 2001
From: Frederik Beimgraben <frederik@beimgraben.net>
Date: Fri, 17 Jan 2025 20:08:38 +0100
Subject: [PATCH] Refactor finding local extrema for performance

---
 .gitignore |  4 +++-
 MMS24-25.c | 56 ++++++++++++++++++++++++++----------------------------
 Makefile   |  2 +-
 tests.c    |  6 ++++++
 4 files changed, 37 insertions(+), 31 deletions(-)

diff --git a/.gitignore b/.gitignore
index f4bc886..9cb28f0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,4 +56,6 @@ main
 
 *results.txt
 
-tests
\ No newline at end of file
+tests
+*.numbered.*
+*.old.*
diff --git a/MMS24-25.c b/MMS24-25.c
index d973c09..26a74e6 100644
--- a/MMS24-25.c
+++ b/MMS24-25.c
@@ -748,19 +748,13 @@ double calculateMedian(double *pdIn, int iLen) {
 /*
  * Creates a new LocalExtrema struct
  */
-LocalExtrema *initLocalExtrema(int *piInPos, int iLen) {
+LocalExtrema *createLocalExtrema() {
     LocalExtrema *localExtrema = (LocalExtrema*) malloc(sizeof(LocalExtrema));
     if (localExtrema == NULL)
         _mem_error("initLocalExtrema: Failed to allocate memory for localExtrema");
 
-    localExtrema->iNumLocalExtrema = iLen;
-    localExtrema->piLocalExtremaPos = (int*) malloc(sizeof(int) *iLen);
-    if (localExtrema->piLocalExtremaPos == NULL)
-        _mem_error("initLocalExtrema: Failed to allocate memory for localExtrema->piLocalExtremaPos");
-
-    for (int i = 0; i < iLen; i++) {
-        localExtrema->piLocalExtremaPos[i] = piInPos[i];
-    }
+    localExtrema->iNumLocalExtrema = 0;
+    localExtrema->piLocalExtremaPos = NULL;
 
     return localExtrema;
 }
@@ -793,56 +787,60 @@ void findLocalExtremaFromArray(
         LocalExtrema **ppexLocalMax,
         LocalExtrema **ppexLocalMin
     ) {
-    int iNumLocalMax = 0;
-    int iNumLocalMin = 0;
-    int *piLocalMaxPos = NULL;
-    int *piLocalMinPos = NULL;
+
+    LocalExtrema *pexLocalMax = createLocalExtrema();
+    LocalExtrema *pexLocalMin = createLocalExtrema();
+
+    int **ppiLocalMaxPos = &pexLocalMax->piLocalExtremaPos;
+    int **ppiLocalMinPos = &pexLocalMin->piLocalExtremaPos;
+    int *iNumLocalMax = &pexLocalMax->iNumLocalExtrema;
+    int *iNumLocalMin = &pexLocalMin->iNumLocalExtrema;
 
     for (int i = 1; i < iLen - 1; i++) {
         if (pdIn[i] > pdIn[i-1] && pdIn[i] > pdIn[i+1]) {
-            iNumLocalMax++;
+            (*iNumLocalMax)++;
 
 #ifdef _DEBUG
             _debug("findLocalExtremaFromArray: Found local maximum at (%d, %lf)", i, pdIn[i]);
 #endif
 
-            if (piLocalMaxPos == NULL)
-                piLocalMaxPos = (int*) malloc(sizeof(int) *iNumLocalMax);
+            if (*ppiLocalMaxPos == NULL)
+                *ppiLocalMaxPos = (int*) malloc(sizeof(int) * (*iNumLocalMax));
             else
-                piLocalMaxPos = (int*) realloc(piLocalMaxPos, sizeof(int) *iNumLocalMax);
+                *ppiLocalMaxPos = (int*) realloc(*ppiLocalMaxPos, sizeof(int) * (*iNumLocalMax));
 
-            if (piLocalMaxPos == NULL)
+            if (*ppiLocalMaxPos == NULL)
                 _mem_error("findLocalExtremaFromArray: Failed to allocate memory for piLocalMaxPos");
 
-            piLocalMaxPos[iNumLocalMax-1] = i;
+            *ppiLocalMaxPos[(*iNumLocalMax)-1] = i;
         }
 
         if (pdIn[i] < pdIn[i-1] && pdIn[i] < pdIn[i+1]) {
-            iNumLocalMin++;
+            (*iNumLocalMin)++;
 
 #ifdef _DEBUG
             _debug("findLocalExtremaFromArray: Found local minimum at (%d, %lf)", i, pdIn[i]);
 #endif
 
-            if (piLocalMinPos == NULL)
-                piLocalMinPos = (int*) malloc(sizeof(int) *iNumLocalMin);
+            if (*ppiLocalMinPos == NULL)
+                *ppiLocalMinPos = (int*) malloc(sizeof(int) * (*iNumLocalMin));
             else
-                piLocalMinPos = (int*) realloc(piLocalMinPos, sizeof(int) *iNumLocalMin);
+                *ppiLocalMinPos = (int*) realloc(*ppiLocalMinPos, sizeof(int) * (*iNumLocalMin));
 
-            if (piLocalMinPos == NULL)
+            if (*ppiLocalMinPos == NULL)
                 _mem_error("findLocalExtremaFromArray: Failed to allocate memory for piLocalMinPos");
 
-            piLocalMinPos[iNumLocalMin-1] = i;
+            *ppiLocalMinPos[(*iNumLocalMin)-1] = i;
         }
     }
 
 #ifdef _DEBUG
-    _debug("findLocalExtremaFromArray: Found %d local maxima", iNumLocalMax);
-    _debug("findLocalExtremaFromArray: Found %d local minima", iNumLocalMin);
+    _debug("findLocalExtremaFromArray: Found %d local maxima", *iNumLocalMax);
+    _debug("findLocalExtremaFromArray: Found %d local minima", *iNumLocalMin);
 #endif
 
-    *ppexLocalMax = initLocalExtrema(piLocalMaxPos, iNumLocalMax);
-    *ppexLocalMin = initLocalExtrema(piLocalMinPos, iNumLocalMin);
+    *ppexLocalMax = pexLocalMax;
+    *ppexLocalMin = pexLocalMin;
 }
 
 /*
diff --git a/Makefile b/Makefile
index bf8468c..f1301eb 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 CC=gcc
 SOURCE_FILE=MMS24-25.c
-OPTS=-lm
+OPTS=-lm -D _DEBUG
 
 all: clean tests run
 
diff --git a/tests.c b/tests.c
index 9ad5137..3141940 100644
--- a/tests.c
+++ b/tests.c
@@ -469,6 +469,12 @@ void testCalcExtrema() {
 
     Extrema *extrema = initExtrema(pdValues, 10);
 
+    info("*extrema: %p", extrema);
+    info("*extrema->pexLocalMax: %p", extrema->pexLocalMax);
+    info("*extrema->pexLocalMin: %p", extrema->pexLocalMin);
+    info("*extrema->pexLocalMax->piLocalExtremaPos: %p", extrema->pexLocalMax->piLocalExtremaPos);
+    info("*extrema->pexLocalMin->piLocalExtremaPos: %p", extrema->pexLocalMin->piLocalExtremaPos);
+
     if (extrema->pexLocalMax->iNumLocalExtrema != 1) {
         error("Failed to calculate the correct number of local maxima: %d != 1", extrema->pexLocalMax->iNumLocalExtrema);
     }