Add alt code for 2000/thadgavin

This version allows for delaying between the writing of characters (for
curses) or pixels (for SDL). I explained how to reconfigure it in the
README.md file.

This is useful for more modern systems as well as if you're sensitive to
rapid swirling.

Typo fixes in README.md.

2000/thadgavin/thadgavin.alt.c

@@ -0,0 +1,93 @@
+
+                      int
+                   X=320      ,Y=200,
+                 n=0,m,     x,y,   j=1024;
+               double     T=44.0     /7,P[
+              333333     ],C[5]       ={ 0,3,
+              0,0,8}      ,p=1,         B=11.0
+               /630,      f=0,r   =     3,g
+                =7,b        =13,*q=P,   D,*J;
+                unsigned               char
+                  U[66666],*v=U,*h,l[5555]
+                       ,c=0,*e,*a,*z;
+
+                    #include <math.h>
+                #define R1(t)   t=(int)(t\
+              *123456789           )%j; t/=j;
+             #define                 Rl(C,t)\
+             n++[C]         =         t*n/12;
+              #define      RI(C)     B=-B; R1\
+              (r)R1(g     )R1(b     )for(n\
+               =0; n<j; ){ Rl(C   ,r)Rl\
+                   (C,g)Rl(C    ,b)++n; }
+
+
+
+       #ifdef __DJGPP__
+         #include <sys/movedata.h>
+               #include <dpmi.h>
+                 #include <pc.h>
+   #define          Q(u,v)         u##portb(0x3##v
+     #define          W        ; Q(out,C9),*h++/4)
+          void       F(int i){  __dpmi_regs r
+           ; if(i){ for(; i>=0; i-=8)while(
+                     ~Q(in,DA) 
+                  )&8^i); for(m=0,z
+              =h+j; h    <z; m     ++){ Q(
+         out,C8),m     )W W W; ++h; } dosmemput
+   (v,X*Y,0xA0000   ); } else{       r.x.ax=
+ 0x13;            __dpmi_int(    0x10,&r); } }
+                   #elif defined(SDL)
+              #include <SDL.h>
+          SDL_Surface    *s; void
+         F(int i){ if   (i){ SDL_SetColors(
+     s,h,0,256);         SDL_UpdateRect
+     (s,0,0,0,        0); usleep(ZS); } else {  SDL_Init( 
+       SDL_INIT_VIDEO); s=SDL_SetVideoMode
+       (X,Y,8,0);       v=s->pixels; } }
+                  #else
+               #include "curses.h"
+             void F(i){ if(i){ for(y=0;
+          y<X*Y                   ; y++)
+         { move  (y/X,y%X);        addch
+        ((*(v   +y)/     32)      [" ."
+        ",:+"   "=@#"   ]); usleep(Z); } ;  refresh
+        (); }     else{          initscr
+        (),x=     COLS&~1,X=x<X?x:X,y=
+         LINES      &~1,Y=y<Y?y:Y; } }
+          #endif
+
+main(int argc, char **argv)
+{
+    F(0);
+
+    for (x=-X/2,y=-Y/2;y<Y/2;++x>=X/2?x=-X/2,y++:4)
+                {*q++ = sqrt(x*x+y*y);
+
+    *q++ = atan2(x,y);
+
+    }for (;n<j*2;l[n++]=0);
+        for(;;)
+        {
+            a=l;z=l+j;e=l+j*2;
+            if ((p+=B)>1){p=2-p;RI(l+j)}
+                        else if (p<0){p=-p;RI(l)}
+
+            while(a<l+j) D=p**a+++(1-p)**z++,*e++=D;
+            h=l+j*2;
+
+            for (J=P,z=v; z<v+X*Y;){
+                D = *J++;
+                *z++=fabs(sin((*J+++C[1])*1.5+D*C[0]+C[2]*sin(C[3]+D/C[4]))*255);
+            }F(8);
+
+            C[2]+=B; f+=T/360; C[3]+=f;
+
+            if (f>T)
+                {C[1] += (f-T)/8;
+
+            if (f>T*2)
+                C[0]=sin(f)+sin(f*2)/2;
+        }
+    }
+}