From 370dee5c07b37fd662d88a10c3c971f7e008cdd4 Mon Sep 17 00:00:00 2001
From: Emile <hanemile@protonmail.com>
Date: Sun, 23 Feb 2020 16:40:04 +0100
Subject: random offsets

---
 src/init.go | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 68 insertions(+), 14 deletions(-)

diff --git a/src/init.go b/src/init.go
index 4b3f2d9..eadf505 100644
--- a/src/init.go
+++ b/src/init.go
@@ -87,10 +87,14 @@ func initArena(config *Config) *r2pipe.Pipe {
 	return r2p
 }
 
-// getRandomOffsets returns random offsets for all bots
+// genRandomOffsets returns random offsets for all bots
 // This is used to get the offset the bots are initially placed in
-func getRandomOffsets(config Config) []int {
+func genRandomOffsets(config *Config) {
 
+	logrus.Info("Generating random bot offsets")
+
+	// define the amount of bots, an array to store the offsets in and a counter
+	// to store the amount of tries it took to find a random positon for the bots
 	var amountOfBots int = len(config.Bots)
 	var offsets []int
 	var roundCounter int = 0
@@ -99,35 +103,85 @@ func getRandomOffsets(config Config) []int {
 	rand.Seed(time.Now().UTC().UnixNano())
 
 	for {
-		// define an integer array to store the random offsets in
-		//var offsets []int = []int{}
+
+		// reset the offsets array
+		offsets = []int{}
 
 		// define a random address
+		// | ------------------------------------- | ----- |
+		// | generate an address in this space
 		address := rand.Intn(config.Memsize - config.MaxProgSize)
+		logrus.Tracef("%d", address)
 
 		// for all bots, try to generate another random address after the intially
 		// generated address and test if it fits in memory
 		for i := 0; i < amountOfBots; i++ {
+
+			// append the address to the offsets array
 			offsets = append(offsets, address)
 
-			// generate a random value in range [maxProgSize, maxProgSize + 300)
-			address += rand.Intn(config.MaxProgSize+300) + config.MaxProgSize
+			// define a min and max bound
+			//
+			// | ------|-|----------------------------------|-|
+			// |       | |           in this space          | |
+			// a       b c                                  d e
+			//
+			// a = 0x0
+			// b = address
+			// c = address + config.MaxProcSize (min)
+			// d = config.Memsize - config.MaxProgSize (max)
+			// e = config.Memsize
+			min := address + config.MaxProgSize
+			max := config.Memsize - config.MaxProgSize
+
+			// if the new minimum bound is bigger or equal to the maximum bound,
+			// discard this try and start with a fresh new initial address
+			if min >= max {
+				roundCounter++
+				break
+			}
+
+			// generate a new address in the [min, max) range defined above
+			address = rand.Intn(max-min) + min
+			logrus.Tracef("%d", address)
 
-			// if there is not enough memory remaining after the last generated
-			// address, start from be beginning
-			if address+config.MaxProgSize > config.Memsize {
+			// If there isn't enough space inbetween the address and the biggest
+			// possible address, as in, the biggest possible bot can't fit in that
+			// space, discard and start with a new fresh initial address
+			if (config.Memsize-config.MaxProgSize)-address < config.MaxProgSize {
 				roundCounter++
-				continue
+				break
 			}
 		}
 
-		// if enough addresses have been generated, break out of the for loop
-		break
+		// if the needed amount of offsets has been found, break out of the infinite loop
+		if len(offsets) == amountOfBots {
+			break
+		}
+	}
+
+	logrus.Infof("Initial bot positions found after %d tries", roundCounter)
+
+	// debug print all offsets
+	var fields0 logrus.Fields = make(logrus.Fields)
+	for i := 0; i < len(offsets); i++ {
+		fields0[fmt.Sprintf("%d", i)] = offsets[i]
 	}
+	logrus.WithFields(fields0).Debug("Offsets")
+
+	// shuffle the offsets
+	rand.Shuffle(len(offsets), func(i, j int) {
+		offsets[i], offsets[j] = offsets[j], offsets[i]
+	})
 
-	log.Printf("[+] Initial bot positions found after %d trues", roundCounter)
+	// debug print the shuffled offsets
+	var fields1 logrus.Fields = make(logrus.Fields)
+	for i := 0; i < len(offsets); i++ {
+		fields1[fmt.Sprintf("%d", i)] = offsets[i]
+	}
+	logrus.WithFields(fields1).Debug("Shuffled offsets")
 
-	return offsets
+	config.RandomOffsets = offsets
 }
 
 // place the bot in the arena at the given address
-- 
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