From 1146f7be49eb2a5abe4db7ba06f568cc81192111 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Sat, 10 Feb 2018 20:49:27 +0100
Subject: Nintendo Rotation System

---
 main.c | 77 +++++++++++++++++++++++++++++++++++-------------------------------
 1 file changed, 41 insertions(+), 36 deletions(-)

diff --git a/main.c b/main.c
index aa4a20e..910b01f 100644
--- a/main.c
+++ b/main.c
@@ -17,26 +17,16 @@
 #define USE_UNICODE
 
 
-const int stones[7]={
-	0b0000000001110001,
-	0b0000000001110100,
-	0b0000000000110011,
-	0b0000000000110110,
-	0b0000000001110010,
-	0b0000000001100011,
-	0b0000000000001111,
+const int stones[7][4]={
+	{0b0000010001110000, 0b0000001100100010, 0b0000000001110001, 0b0000001000100110},
+	{0b0000000101110000, 0b0000001000100011, 0b0000000001110100, 0b0000011000100010},
+	{0b0000001101100000, 0b0000010001100010, 0b0000001101100000, 0b0000010001100010},
+	{0b0000001001110000, 0b0000001000110010, 0b0000000001110010, 0b0000001001100010},
+	{0b0000011000110000, 0b0000001001100100, 0b0000011000110000, 0b0000001001100100},
+	{0b0000111100000000, 0b0100010001000100, 0b0000111100000000, 0b0100010001000100},
+	{0b0000011001100000, 0b0000011001100000, 0b0000011001100000, 0b0000011001100000},
 };
 
-static int rotateR(int bl){
-	int dest=0;
-	for(int y=0;y<4;y++){
-		for(int x=0;x<4;x++){
-			dest|=(!!(bl&(1<<(4*y+x))))<<(4*x+3-y);
-		}
-	}
-	return dest;
-}
-
 static int leveldelay(int level){
 	int d=700-(level-1)*35;
 	if(d<50)d=50;
@@ -46,38 +36,51 @@ static int leveldelay(int level){
 
 struct board {
 	int lines[HEI];
-	int stone,stx,sty;
+	int stone,str,stx,sty;
 
 	int ncleared,level,delay;
 };
 
 static bool boardvalid(const struct board *bd){
+	int st=stones[bd->stone][bd->str];
 	for(int y=0;y<4;y++){
 		for(int x=0;x<4;x++){
-			if((bd->stone&(1<<(4*y+x)))){
+			int bit=1<<(4*y+x);
+			if(st&bit){
 				if(bd->sty+y>=HEI)return false;
 				if(bd->stx+x<0||bd->stx+x>=WID)return false;
 			}
-			if(bd->lines[bd->sty+y]&((!!(bd->stone&(1<<(4*y+x))))<<(bd->stx+x)))return false;
+			if(bd->lines[bd->sty+y]&((!!(st&bit))<<(bd->stx+x)))return false;
 		}
 	}
 	return true;
 }
 
 static void persist(struct board *bd){
+	int st=stones[bd->stone][bd->str];
 	for(int y=0;y<4;y++){
 		for(int x=0;x<4;x++){
-			bd->lines[bd->sty+y]|=(!!(bd->stone&(1<<(4*y+x))))<<(bd->stx+x);
+			bd->lines[bd->sty+y]|=(!!(st&(1<<(4*y+x))))<<(bd->stx+x);
 		}
 	}
 }
 
+// [0,mx)
+static int randomrange(unsigned int mx){
+	assert(mx<=(unsigned int)RAND_MAX+1);
+	unsigned int diff=((unsigned int)RAND_MAX+1)%mx;
+	unsigned int r=random();
+	// happens at most 50% of the time
+	if(r>RAND_MAX-diff)return randomrange(mx);
+	return r%mx;
+}
+
 // returns false iff game over
 static bool spawn(struct board *bd){
-	int idx=random()%7;
-	bd->stone=stones[idx];
+	bd->stone=randomrange(7);
+	bd->str=random()%4;
 	bd->stx=WID/2-1;
-	bd->sty=0;
+	for(bd->sty=0;(stones[bd->stone][bd->str]&((1<<(4+4*-bd->sty))-1))==0;bd->sty--);
 	return boardvalid(bd);
 }
 
@@ -146,7 +149,7 @@ static void checklines(struct board *bd){
 
 // returns false iff game over
 static bool advance(struct board *bd){
-	if(bd->stone==0){
+	if(bd->stone<0){
 		return spawn(bd);
 	}
 	bd->sty++;
@@ -165,9 +168,13 @@ static void move(struct board *bd,int dir){
 }
 
 static void rotR(struct board *bd){
-	int st=bd->stone;
-	bd->stone=rotateR(bd->stone);
-	if(!boardvalid(bd))bd->stone=st;
+	bd->str=(bd->str+1)%4;
+	if(!boardvalid(bd))bd->str=(bd->str+3)%4;
+}
+
+static void delaytimeout(const struct board *bd,struct timeval *tv){
+	tv->tv_sec=bd->delay/1000;
+	tv->tv_usec=bd->delay%1000*1000;
 }
 
 
@@ -186,14 +193,14 @@ int main(void){
 
 	struct board bd;
 	memset(&bd,0,sizeof bd);
+	bd.stone=-1;
 	bd.ncleared=0;
 	bd.level=1;
 	bd.delay=leveldelay(bd.level);
-	show(&bd);
+	spawn(&bd);
 
 	struct timeval timeleft;
-	timeleft.tv_sec=0;
-	timeleft.tv_usec=0;
+	delaytimeout(&bd,&timeleft);
 
 	while(true){
 		show(&bd);
@@ -223,8 +230,7 @@ int main(void){
 
 		if(ret==0){
 			if(!advance(&bd))break;
-			timeleft.tv_sec=bd.delay/1000;
-			timeleft.tv_usec=bd.delay%1000*1000;
+			delaytimeout(&bd,&timeleft);
 			continue;
 		}
 		end.tv_sec-=start.tv_sec;
@@ -250,8 +256,7 @@ int main(void){
 			if(key=='Q'||key=='q')break;
 			else if(key=='S'||key=='s'||key==KEY_DOWN){
 				if(!advance(&bd))break;
-				timeleft.tv_sec=bd.delay/1000;
-				timeleft.tv_usec=bd.delay%1000*1000;
+				delaytimeout(&bd,&timeleft);
 			} else if(key=='A'||key=='a'||key==KEY_LEFT)move(&bd,-1);
 			else if(key=='D'||key=='d'||key==KEY_RIGHT)move(&bd,1);
 			else if(key=='W'||key=='w'||key==KEY_UP)rotR(&bd);
-- 
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