experimental/Intersection/CubicParameterizationCode.cpp - platform/external/skqp - Gitiles

 #include <vector>

 /* Given:
  * Resultant[a*t^3 + b*t^2 + c*t + d - x, e*t^3 + f*t^2 + g*t + h - y, t]
  */

 const char result1[] =
 "-d^3 e^3 + c d^2 e^2 f - b d^2 e f^2 + a d^2 f^3 - c^2 d e^2 g + "
 " 2 b d^2 e^2 g + b c d e f g - 3 a d^2 e f g - a c d f^2 g - "
 " b^2 d e g^2 + 2 a c d e g^2 + a b d f g^2 - a^2 d g^3 + c^3 e^2 h - "
 " 3 b c d e^2 h + 3 a d^2 e^2 h - b c^2 e f h + 2 b^2 d e f h + "
 " a c d e f h + a c^2 f^2 h - 2 a b d f^2 h + b^2 c e g h - "
 " 2 a c^2 e g h - a b d e g h - a b c f g h + 3 a^2 d f g h + "
 " a^2 c g^2 h - b^3 e h^2 + 3 a b c e h^2 - 3 a^2 d e h^2 + "
 " a b^2 f h^2 - 2 a^2 c f h^2 - a^2 b g h^2 + a^3 h^3 + 3 d^2 e^3 x - "
 " 2 c d e^2 f x + 2 b d e f^2 x - 2 a d f^3 x + c^2 e^2 g x - "
 " 4 b d e^2 g x - b c e f g x + 6 a d e f g x + a c f^2 g x + "
 " b^2 e g^2 x - 2 a c e g^2 x - a b f g^2 x + a^2 g^3 x + "
 " 3 b c e^2 h x - 6 a d e^2 h x - 2 b^2 e f h x - a c e f h x + "
 " 2 a b f^2 h x + a b e g h x - 3 a^2 f g h x + 3 a^2 e h^2 x - "
 " 3 d e^3 x^2 + c e^2 f x^2 - b e f^2 x^2 + a f^3 x^2 + "
 " 2 b e^2 g x^2 - 3 a e f g x^2 + 3 a e^2 h x^2 + e^3 x^3 - "
 " c^3 e^2 y + 3 b c d e^2 y - 3 a d^2 e^2 y + b c^2 e f y - "
 " 2 b^2 d e f y - a c d e f y - a c^2 f^2 y + 2 a b d f^2 y - "
 " b^2 c e g y + 2 a c^2 e g y + a b d e g y + a b c f g y - "
 " 3 a^2 d f g y - a^2 c g^2 y + 2 b^3 e h y - 6 a b c e h y + "
 " 6 a^2 d e h y - 2 a b^2 f h y + 4 a^2 c f h y + 2 a^2 b g h y - "
 " 3 a^3 h^2 y - 3 b c e^2 x y + 6 a d e^2 x y + 2 b^2 e f x y + "
 " a c e f x y - 2 a b f^2 x y - a b e g x y + 3 a^2 f g x y - "
 " 6 a^2 e h x y - 3 a e^2 x^2 y - b^3 e y^2 + 3 a b c e y^2 - "
 " 3 a^2 d e y^2 + a b^2 f y^2 - 2 a^2 c f y^2 - a^2 b g y^2 + "
 " 3 a^3 h y^2 + 3 a^2 e x y^2 - a^3 y^3";

 const size_t len1 = sizeof(result1) - 1;

 /* Given:
  * Expand[
  * Det[{{a, b, c, (d - x),      0,      0},
  *      {0, a, b,      c,  (d - x),     0},
  *      {0, 0, a,      b,       c, (d - x)},
  *      {e, f, g, (h - y),      0,      0},
  *      {0, e, f,      g,  (h - y),     0},
  *      {0, 0, e,      f,       g, (h - y)}}]]
  */
  // result1 and result2 are the same. 102 factors:
 const char result2[] =
 "-d^3 e^3       + c d^2 e^2 f   - b d^2 e f^2   + a d^2 f^3     - c^2 d e^2 g + "
 " 2 b d^2 e^2 g + b c d e f g   - 3 a d^2 e f g - a c d f^2 g   - "
 " b^2 d e g^2   + 2 a c d e g^2 + a b d f g^2   - a^2 d g^3     + c^3 e^2 h - "
 " 3 b c d e^2 h + 3 a d^2 e^2 h - b c^2 e f h   + 2 b^2 d e f h + "
 " a c d e f h   + a c^2 f^2 h   - 2 a b d f^2 h + b^2 c e g h   - "
 " 2 a c^2 e g h - a b d e g h   - a b c f g h   + 3 a^2 d f g h + "
 " a^2 c g^2 h   - b^3 e h^2     + 3 a b c e h^2 - 3 a^2 d e h^2 + "
 " a b^2 f h^2   - 2 a^2 c f h^2 - a^2 b g h^2   + a^3 h^3       + 3 d^2 e^3 x - "
 " 2 c d e^2 f x + 2 b d e f^2 x - 2 a d f^3 x   + c^2 e^2 g x   - "
 " 4 b d e^2 g x - b c e f g x   + 6 a d e f g x + a c f^2 g x   + "
 " b^2 e g^2 x   - 2 a c e g^2 x - a b f g^2 x   + a^2 g^3 x     + "
 " 3 b c e^2 h x - 6 a d e^2 h x - 2 b^2 e f h x - a c e f h x   + "
 " 2 a b f^2 h x + a b e g h x   - 3 a^2 f g h x + 3 a^2 e h^2 x - "
 " 3 d e^3 x^2   + c e^2 f x^2   - b e f^2 x^2   + a f^3 x^2     + "
 " 2 b e^2 g x^2 - 3 a e f g x^2 + 3 a e^2 h x^2 + e^3 x^3       - "
 " c^3 e^2 y     + 3 b c d e^2 y - 3 a d^2 e^2 y + b c^2 e f y   - "
 " 2 b^2 d e f y - a c d e f y   - a c^2 f^2 y   + 2 a b d f^2 y - "
 " b^2 c e g y   + 2 a c^2 e g y + a b d e g y   + a b c f g y   - "
 " 3 a^2 d f g y - a^2 c g^2 y   + 2 b^3 e h y   - 6 a b c e h y + "
 " 6 a^2 d e h y - 2 a b^2 f h y + 4 a^2 c f h y + 2 a^2 b g h y - "
 " 3 a^3 h^2 y   - 3 b c e^2 x y + 6 a d e^2 x y + 2 b^2 e f x y + "
 " a c e f x y   - 2 a b f^2 x y - a b e g x y   + 3 a^2 f g x y - "
 " 6 a^2 e h x y - 3 a e^2 x^2 y - b^3 e y^2     + 3 a b c e y^2 - "
 " 3 a^2 d e y^2 + a b^2 f y^2   - 2 a^2 c f y^2 - a^2 b g y^2   + "
 " 3 a^3 h y^2   + 3 a^2 e x y^2 - a^3 y^3";

 const size_t len2 = sizeof(result2) - 1;

 /* Given: r1 = Resultant[
  *      a*(1 - t)^3 + 3*b*(1 - t)^2*t + 3*c*(1 - t)*t^2 + d*t^3 - x,
  *      e*(1 - t)^3 + 3*f*(1 - t)^2*t + 3*g*(1 - t)*t^2 + h*t^3 - y, t]
  *        Collect[r1, {x, y}, Simplify]
  *        CForm[%]
  *      then use regex to replace Power\(([a-h]),3\) with \1*\1*\1
  *                            and Power\(([a-h]),2\) with \1*\1
  * yields:

 d*d*d*e*e*e - 3*d*d*(3*c*e*e*f + 3*b*e*(-3*f*f + 2*e*g) + a*(9*f*f*f - 9*e*f*g + e*e*h)) -
    h*(27*c*c*c*e*e - 27*c*c*(3*b*e*f - 3*a*f*f + 2*a*e*g) +
       h*(-27*b*b*b*e + 27*a*b*b*f - 9*a*a*b*g + a*a*a*h) +
       9*c*(9*b*b*e*g + a*b*(-9*f*g + 3*e*h) + a*a*(3*g*g - 2*f*h))) +
    3*d*(9*c*c*e*e*g + 9*b*b*e*(3*g*g - 2*f*h) + 3*a*b*(-9*f*g*g + 6*f*f*h + e*g*h) +
       a*a*(9*g*g*g - 9*f*g*h + e*h*h) + 3*c*(3*b*e*(-3*f*g + e*h) + a*(9*f*f*g - 6*e*g*g - e*f*h)))

 - Power(e - 3*f + 3*g - h,3)*Power(x,3)

 + 3*(6*b*d*d*e*e - d*d*d*e*e + 18*b*b*d*e*f - 18*b*d*d*e*f -
       9*b*d*d*f*f - 54*b*b*d*e*g + 12*b*d*d*e*g - 27*b*b*d*g*g - 18*b*b*b*e*h + 18*b*b*d*e*h +
       18*b*b*d*f*h + a*a*a*h*h - 9*b*b*b*h*h + 9*c*c*c*e*(e + 2*h) +
       a*a*(-3*b*h*(2*g + h) + d*(-27*g*g + 9*g*h - h*(2*e + h) + 9*f*(g + h))) +
       a*(9*b*b*h*(2*f + h) - 3*b*d*(6*f*f - 6*f*(3*g - 2*h) + g*(-9*g + h) + e*(g + h)) +
          d*d*(e*e + 9*f*(3*f - g) + e*(-9*f - 9*g + 2*h))) -
       9*c*c*(d*e*(e + 2*g) + 3*b*(f*h + e*(f + h)) + a*(-3*f*f - 6*f*h + 2*(g*h + e*(g + h)))) +
       3*c*(d*d*e*(e + 2*f) + a*a*(3*g*g + 6*g*h - 2*h*(2*f + h)) + 9*b*b*(g*h + e*(g + h)) +
          a*d*(-9*f*f - 18*f*g + 6*g*g + f*h + e*(f + 12*g + h)) +
          b*(d*(-3*e*e + 9*f*g + e*(9*f + 9*g - 6*h)) + 3*a*(h*(2*e - 3*g + h) - 3*f*(g + h)))))*y

 - 3*(18*c*c*c*e - 18*c*c*d*e + 6*c*d*d*e - d*d*d*e + 3*c*d*d*f - 9*c*c*d*g + a*a*a*h + 9*c*c*c*h -
       9*b*b*b*(e + 2*h) - a*a*(d*(e - 9*f + 18*g - 7*h) + 3*c*(2*f - 6*g + h)) +
       a*(-9*c*c*(2*e - 6*f + 2*g - h) + d*d*(-7*e + 18*f - 9*g + h) + 3*c*d*(7*e - 17*f + 3*g + h)) +
       9*b*b*(3*c*(e + g + h) + a*(f + 2*h) - d*(e - 2*(f - 3*g + h))) -
       3*b*(-(d*d*(e - 6*f + 2*g)) - 3*c*d*(e + 3*f + 3*g - h) + 9*c*c*(e + f + h) + a*a*(g + 2*h) +
          a*(c*(-3*e + 9*f + 9*g + 3*h) + d*(e + 3*f - 17*g + 7*h))))*Power(y,2)

 + Power(a - 3*b + 3*c - d,3)*Power(y,3)

 + Power(x,2)*(-3*(-9*b*e*f*f + 9*a*f*f*f + 6*b*e*e*g - 9*a*e*f*g + 27*b*e*f*g - 27*a*f*f*g + 18*a*e*g*g - 54*b*e*g*g +
          27*a*f*g*g + 27*b*f*g*g - 18*a*g*g*g + a*e*e*h - 9*b*e*e*h + 3*a*e*f*h + 9*b*e*f*h + 9*a*f*f*h -
          18*b*f*f*h - 21*a*e*g*h + 51*b*e*g*h - 9*a*f*g*h - 27*b*f*g*h + 18*a*g*g*h + 7*a*e*h*h - 18*b*e*h*h - 3*a*f*h*h +
          18*b*f*h*h - 6*a*g*h*h - 3*b*g*h*h + a*h*h*h +
          3*c*(-9*f*f*(g - 2*h) + 3*g*g*h - f*h*(9*g + 2*h) + e*e*(f - 6*g + 6*h) +
             e*(9*f*g + 6*g*g - 17*f*h - 3*g*h + 3*h*h)) -
          d*(e*e*e + e*e*(-6*f - 3*g + 7*h) - 9*(2*f - g)*(f*f + g*g - f*(g + h)) +
             e*(18*f*f + 9*g*g + 3*g*h + h*h - 3*f*(3*g + 7*h)))) )

 + Power(x,2)*(3*(a - 3*b + 3*c - d)*Power(e - 3*f + 3*g - h,2)*y)

 + x*(-3*(27*b*b*e*g*g - 27*a*b*f*g*g + 9*a*a*g*g*g - 18*b*b*e*f*h + 18*a*b*f*f*h + 3*a*b*e*g*h -
          27*b*b*e*g*h - 9*a*a*f*g*h + 27*a*b*f*g*h - 9*a*a*g*g*h + a*a*e*h*h - 9*a*b*e*h*h +
          27*b*b*e*h*h + 6*a*a*f*h*h - 18*a*b*f*h*h - 9*b*b*f*h*h + 3*a*a*g*h*h +
          6*a*b*g*h*h - a*a*h*h*h + 9*c*c*(e*e*(g - 3*h) - 3*f*f*h + e*(3*f + 2*g)*h) +
          d*d*(e*e*e - 9*f*f*f + 9*e*f*(f + g) - e*e*(3*f + 6*g + h)) +
          d*(-3*c*(-9*f*f*g + e*e*(2*f - 6*g - 3*h) + e*(9*f*g + 6*g*g + f*h)) +
             a*(-18*f*f*f - 18*e*g*g + 18*g*g*g - 2*e*e*h + 3*e*g*h + 2*e*h*h + 9*f*f*(3*g + 2*h) +
                3*f*(6*e*g - 9*g*g - e*h - 6*g*h)) - 3*b*(9*f*g*g + e*e*(4*g - 3*h) - 6*f*f*h -
                e*(6*f*f + g*(18*g + h) - 3*f*(3*g + 4*h)))) +
          3*c*(3*b*(e*e*h + 3*f*g*h - e*(3*f*g - 6*f*h + 6*g*h + h*h)) +
             a*(9*f*f*(g - 2*h) + f*h*(-e + 9*g + 4*h) - 3*(2*g*g*h + e*(2*g*g - 4*g*h + h*h))))) )

 + x*3*(-2*a*d*e*e - 7*d*d*e*e + 15*a*d*e*f + 21*d*d*e*f - 9*a*d*f*f - 18*d*d*f*f - 15*a*d*e*g -
          3*d*d*e*g - 9*a*a*f*g + 9*d*d*f*g + 18*a*a*g*g + 9*a*d*g*g + 2*a*a*e*h - 2*d*d*e*h +
          3*a*a*f*h + 15*a*d*f*h - 21*a*a*g*h - 15*a*d*g*h + 7*a*a*h*h + 2*a*d*h*h -
          9*c*c*(2*e*e + 3*f*f + 3*f*h - 2*g*h + e*(-3*f - 4*g + h)) +
          9*b*b*(3*g*g - 3*g*h + 2*h*(-2*f + h) + e*(-2*f + 3*g + h)) +
          3*b*(3*c*(e*e + 3*e*(f - 3*g) + (9*f - 3*g - h)*h) + a*(6*f*f + e*g - 9*f*g - 9*g*g - 5*e*h + 9*f*h + 14*g*h - 7*h*h) +
             d*(-e*e + 12*f*f - 27*f*g + e*(-9*f + 20*g - 5*h) + g*(9*g + h))) +
          3*c*(a*(-(e*f) - 9*f*f + 27*f*g - 12*g*g + 5*e*h - 20*f*h + 9*g*h + h*h) +
             d*(7*e*e + 9*f*f + 9*f*g - 6*g*g - f*h + e*(-14*f - 9*g + 5*h))))*y

 - x*3*Power(a - 3*b + 3*c - d,2)*(e - 3*f + 3*g - h)*Power(y,2)

 */

 const int factors = 8;

 struct coeff {
     int s; // constant and coefficient sign
     int n[factors]; // 0 or power of a (1, 2, or 3) for a through h
 };

 enum {
     xxx_coeff,
     xxy_coeff,
     xyy_coeff,
     yyy_coeff,
     xx_coeff,
     xy_coeff,
     yy_coeff,
     x_coeff,
     y_coeff,
     c_coeff,
     coeff_count
 };

 typedef std::vector<coeff> coeffs;
 typedef std::vector<coeffs> n_coeffs;

 static char skipSpace(const char* str, size_t& index) {
     do {
         ++index;
     } while (str[index] == ' ');
     return str[index];
 }

 static char backSkipSpace(const char* str, size_t& end) {
     while (str[end - 1] == ' ') {
         --end;
     }
     return str[end - 1];
 }

 static void match(const char* str, size_t len, coeffs& co, const char pattern[]) {
     size_t patternLen = strlen(pattern);
     size_t index = 0;
     while (index < len) {
         char ch = str[index];
         if (ch != '-' && ch != '+') {
             printf("missing sign\n");
         }
         size_t end = index + 1;
         while (str[end] != '+' && str[end] != '-' && ++end < len) {
             ;
         }
         backSkipSpace(str, end);
         size_t idx = index;
         index = end;
         skipSpace(str, index);
         if (!strncmp(&str[end - patternLen], pattern, patternLen) == 0) {
             continue;
         }
         size_t endCoeff = end - patternLen;
         char last = backSkipSpace(str, endCoeff);
         if (last == '2' || last == '3') {
             last = str[endCoeff - 3]; // skip ^2
         }
         if (last == 'x' || last == 'y') {
             continue;
         }
         coeff c;
         c.s = str[idx] == '-' ? -1 : 1;
         bzero(c.n, sizeof(c.n));
         ch = skipSpace(str, idx);
         if (ch >= '2' && ch <= '6') {
             c.s *= ch - '0';
             ch = skipSpace(str, idx);
         }
         while (idx < endCoeff) {
             char x = str[idx];
             if (x < 'a' || x > 'a' + factors) {
                 printf("expected factor\n");
             }
             idx++;
             int pow = 1;
             if (str[idx] == '^') {
                 idx++;
                 char exp = str[idx];
                 if (exp < '2' || exp > '3') {
                     printf("expected exponent\n");
                 }
                 pow = exp - '0';
             }
             skipSpace(str, idx);
             c.n[x - 'a'] = pow;
         }
         co.push_back(c);
     }
 }

 void cubecode_test(int test);

 void cubecode_test(int test) {
     const char* str = test ? result2 : result1;
     size_t len = strlen(str);
     n_coeffs c(coeff_count);
     match(str, len, c[xxx_coeff], "x^3");   // 1 factor
     match(str, len, c[xxy_coeff], "x^2 y"); // 1 factor
     match(str, len, c[xyy_coeff], "x y^2"); // 1 factor
     match(str, len, c[yyy_coeff], "y^3");   // 1 factor
     match(str, len, c[xx_coeff], "x^2");    // 7 factors
     match(str, len, c[xy_coeff], "x y");    // 8 factors
     match(str, len, c[yy_coeff], "y^2");    // 7 factors
     match(str, len, c[x_coeff], "x");       // 21 factors
     match(str, len, c[y_coeff], "y");       // 21 factors
     match(str, len, c[c_coeff], "");        // 34 factors : total 102
 #define COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS 0
 #define WRITE_AS_NONOPTIMIZED_C_CODE 0
 #if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
     int count[factors][factors][factors];
     bzero(count, sizeof(count));
 #endif
 #if WRITE_AS_NONOPTIMIZED_C_CODE
     printf("// start of generated code");
 #endif
     for (n_coeffs::iterator it = c.begin(); it < c.end(); ++it) {
         coeffs& co = *it;
 #if WRITE_AS_NONOPTIMIZED_C_CODE
         printf("\nstatic double calc_%c(double a, double b, double c, double d,"
                "\n                     double e, double f, double g, double h) {"
                "\n    return"
                "\n ", 'A' + (it - c.begin()));
         if (co[0].s > 0) {
             printf(" ");
         }
         if (abs(co[0].s) == 1) {
             printf("    ");
         }
 #endif
         for (coeffs::iterator ct = co.begin(); ct < co.end(); ++ct) {
             const coeff& cf = *ct;
 #if WRITE_AS_NONOPTIMIZED_C_CODE
             printf("        ");
             bool firstFactor = false;
             if (ct - co.begin() > 0 || cf.s < 0) {
                 printf("%c", cf.s < 0 ? '-' : '+');
             }
             if (ct - co.begin() > 0) {
                 printf(" ");
             }
             if (abs(cf.s) > 1) {
                 printf("%d * ", abs(cf.s));
             } else {
                 if (ct - co.begin() > 0) {
                     printf("    ");
                 }
             }
 #endif
             for (int x = 0; x < factors; ++x) {
                 if (cf.n[x] == 0) {
                     continue;
                 }
 #if WRITE_AS_NONOPTIMIZED_C_CODE
                 for (int y = 0 ; y < cf.n[x]; ++y) {
                     if (y > 0 || firstFactor) {
                         printf(" * ");
                     }
                     printf("%c", 'a' + x);
                 }
                 firstFactor = true;
 #endif
 #if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
                 for (int y = x; y < factors; ++y) {
                     if (cf.n[y] == 0) {
                         continue;
                     }
                     if (x == y && cf.n[y] == 1) {
                         continue;
                     }
                     for (int z = y; z < factors; ++z) {
                         if (cf.n[z] == 0) {
                             continue;
                         }
                         if ((x == z || y == z) && cf.n[z] == 1) {
                             continue;
                         }
                         if (x == y && y == z && cf.n[z] == 2) {
                             continue;
                         }
                         count[x][y][z]++;
                     }
                 }
 #endif
             }
 #if WRITE_AS_NONOPTIMIZED_C_CODE
             if (ct + 1 < co.end()) {
                 printf("\n");
             }
 #endif
         }
 #if WRITE_AS_NONOPTIMIZED_C_CODE
             printf(";\n}\n");
 #endif
     }
 #if WRITE_AS_NONOPTIMIZED_C_CODE
     printf("// end of generated code\n");
 #endif
 #if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
     const int bestCount = 20;
     int best[bestCount][4];
     bzero(best, sizeof(best));
     for (int x = 0; x < factors; ++x) {
         for (int y = x; y < factors; ++y) {
             for (int z = y; z < factors; ++z) {
                 if (!count[x][y][z]) {
                     continue;
                 }
                 for (int w = 0; w < bestCount; ++w) {
                     if (best[w][0] < count[x][y][z]) {
                         best[w][0] = count[x][y][z];
                         best[w][1] = x;
                         best[w][2] = y;
                         best[w][3] = z;
                         break;
                     }
                 }
             }
         }
     }
     for (int w = 0; w < bestCount; ++w) {
         printf("%c%c%c=%d\n", 'a' + best[w][1], 'a'  + best[w][2],
             'a' + best[w][3], best[w][0]);
     }
 #endif
 #if WRITE_AS_NONOPTIMIZED_C_CODE
     printf("\n");
 #endif
 }

 /* results: variable triplets used 10 or more times:
 aah=14
 ade=14
 aeh=14
 dee=14
 bce=13
 beg=13
 beh=12
 bbe=11
 bef=11
 cee=11
 cef=11
 def=11
 ceh=10
 deg=10
 */
	#include <vector>

	/* Given:
	* Resultant[at^3 + bt^2 + ct + d - x, et^3 + ft^2 + gt + h - y, t]
	*/

	const char result1[] =
	"-d^3 e^3 + c d^2 e^2 f - b d^2 e f^2 + a d^2 f^3 - c^2 d e^2 g + "
	" 2 b d^2 e^2 g + b c d e f g - 3 a d^2 e f g - a c d f^2 g - "
	" b^2 d e g^2 + 2 a c d e g^2 + a b d f g^2 - a^2 d g^3 + c^3 e^2 h - "
	" 3 b c d e^2 h + 3 a d^2 e^2 h - b c^2 e f h + 2 b^2 d e f h + "
	" a c d e f h + a c^2 f^2 h - 2 a b d f^2 h + b^2 c e g h - "
	" 2 a c^2 e g h - a b d e g h - a b c f g h + 3 a^2 d f g h + "
	" a^2 c g^2 h - b^3 e h^2 + 3 a b c e h^2 - 3 a^2 d e h^2 + "
	" a b^2 f h^2 - 2 a^2 c f h^2 - a^2 b g h^2 + a^3 h^3 + 3 d^2 e^3 x - "
	" 2 c d e^2 f x + 2 b d e f^2 x - 2 a d f^3 x + c^2 e^2 g x - "
	" 4 b d e^2 g x - b c e f g x + 6 a d e f g x + a c f^2 g x + "
	" b^2 e g^2 x - 2 a c e g^2 x - a b f g^2 x + a^2 g^3 x + "
	" 3 b c e^2 h x - 6 a d e^2 h x - 2 b^2 e f h x - a c e f h x + "
	" 2 a b f^2 h x + a b e g h x - 3 a^2 f g h x + 3 a^2 e h^2 x - "
	" 3 d e^3 x^2 + c e^2 f x^2 - b e f^2 x^2 + a f^3 x^2 + "
	" 2 b e^2 g x^2 - 3 a e f g x^2 + 3 a e^2 h x^2 + e^3 x^3 - "
	" c^3 e^2 y + 3 b c d e^2 y - 3 a d^2 e^2 y + b c^2 e f y - "
	" 2 b^2 d e f y - a c d e f y - a c^2 f^2 y + 2 a b d f^2 y - "
	" b^2 c e g y + 2 a c^2 e g y + a b d e g y + a b c f g y - "
	" 3 a^2 d f g y - a^2 c g^2 y + 2 b^3 e h y - 6 a b c e h y + "
	" 6 a^2 d e h y - 2 a b^2 f h y + 4 a^2 c f h y + 2 a^2 b g h y - "
	" 3 a^3 h^2 y - 3 b c e^2 x y + 6 a d e^2 x y + 2 b^2 e f x y + "
	" a c e f x y - 2 a b f^2 x y - a b e g x y + 3 a^2 f g x y - "
	" 6 a^2 e h x y - 3 a e^2 x^2 y - b^3 e y^2 + 3 a b c e y^2 - "
	" 3 a^2 d e y^2 + a b^2 f y^2 - 2 a^2 c f y^2 - a^2 b g y^2 + "
	" 3 a^3 h y^2 + 3 a^2 e x y^2 - a^3 y^3";

	const size_t len1 = sizeof(result1) - 1;

	/* Given:
	* Expand[
	* Det[{{a, b, c, (d - x), 0, 0},
	* {0, a, b, c, (d - x), 0},
	* {0, 0, a, b, c, (d - x)},
	* {e, f, g, (h - y), 0, 0},
	* {0, e, f, g, (h - y), 0},
	* {0, 0, e, f, g, (h - y)}}]]
	*/
	// result1 and result2 are the same. 102 factors:
	const char result2[] =
	"-d^3 e^3 + c d^2 e^2 f - b d^2 e f^2 + a d^2 f^3 - c^2 d e^2 g + "
	" 2 b d^2 e^2 g + b c d e f g - 3 a d^2 e f g - a c d f^2 g - "
	" b^2 d e g^2 + 2 a c d e g^2 + a b d f g^2 - a^2 d g^3 + c^3 e^2 h - "
	" 3 b c d e^2 h + 3 a d^2 e^2 h - b c^2 e f h + 2 b^2 d e f h + "
	" a c d e f h + a c^2 f^2 h - 2 a b d f^2 h + b^2 c e g h - "
	" 2 a c^2 e g h - a b d e g h - a b c f g h + 3 a^2 d f g h + "
	" a^2 c g^2 h - b^3 e h^2 + 3 a b c e h^2 - 3 a^2 d e h^2 + "
	" a b^2 f h^2 - 2 a^2 c f h^2 - a^2 b g h^2 + a^3 h^3 + 3 d^2 e^3 x - "
	" 2 c d e^2 f x + 2 b d e f^2 x - 2 a d f^3 x + c^2 e^2 g x - "
	" 4 b d e^2 g x - b c e f g x + 6 a d e f g x + a c f^2 g x + "
	" b^2 e g^2 x - 2 a c e g^2 x - a b f g^2 x + a^2 g^3 x + "
	" 3 b c e^2 h x - 6 a d e^2 h x - 2 b^2 e f h x - a c e f h x + "
	" 2 a b f^2 h x + a b e g h x - 3 a^2 f g h x + 3 a^2 e h^2 x - "
	" 3 d e^3 x^2 + c e^2 f x^2 - b e f^2 x^2 + a f^3 x^2 + "
	" 2 b e^2 g x^2 - 3 a e f g x^2 + 3 a e^2 h x^2 + e^3 x^3 - "
	" c^3 e^2 y + 3 b c d e^2 y - 3 a d^2 e^2 y + b c^2 e f y - "
	" 2 b^2 d e f y - a c d e f y - a c^2 f^2 y + 2 a b d f^2 y - "
	" b^2 c e g y + 2 a c^2 e g y + a b d e g y + a b c f g y - "
	" 3 a^2 d f g y - a^2 c g^2 y + 2 b^3 e h y - 6 a b c e h y + "
	" 6 a^2 d e h y - 2 a b^2 f h y + 4 a^2 c f h y + 2 a^2 b g h y - "
	" 3 a^3 h^2 y - 3 b c e^2 x y + 6 a d e^2 x y + 2 b^2 e f x y + "
	" a c e f x y - 2 a b f^2 x y - a b e g x y + 3 a^2 f g x y - "
	" 6 a^2 e h x y - 3 a e^2 x^2 y - b^3 e y^2 + 3 a b c e y^2 - "
	" 3 a^2 d e y^2 + a b^2 f y^2 - 2 a^2 c f y^2 - a^2 b g y^2 + "
	" 3 a^3 h y^2 + 3 a^2 e x y^2 - a^3 y^3";

	const size_t len2 = sizeof(result2) - 1;

	/* Given: r1 = Resultant[
	* a(1 - t)^3 + 3b(1 - t)^2t + 3c(1 - t)t^2 + dt^3 - x,
	* e(1 - t)^3 + 3f(1 - t)^2t + 3g(1 - t)t^2 + ht^3 - y, t]
	* Collect[r1, {x, y}, Simplify]
	* CForm[%]
	* then use regex to replace Power\(([a-h]),3\) with \1\1\1
	* and Power\(([a-h]),2\) with \1*\1
	* yields:

	dddeee - 3dd(3ceef + 3be(-3ff + 2eg) + a(9fff - 9efg + eeh)) -
	h(27cccee - 27cc(3bef - 3aff + 2aeg) +
	h(-27bbbe + 27abbf - 9aabg + aaah) +
	9c(9bbeg + ab(-9fg + 3eh) + aa(3gg - 2fh))) +
	3d(9cceeg + 9bbe(3gg - 2fh) + 3ab(-9fgg + 6ffh + egh) +
	aa(9ggg - 9fgh + ehh) + 3c(3be(-3fg + eh) + a(9ffg - 6egg - ef*h)))

	- Power(e - 3f + 3g - h,3)*Power(x,3)

	+ 3(6bddee - dddee + 18bbdef - 18bddef -
	9bddff - 54bbdeg + 12bddeg - 27bbdgg - 18bbbeh + 18bbdeh +
	18bbdfh + aaahh - 9bbbhh + 9ccce(e + 2h) +
	aa(-3bh(2g + h) + d(-27gg + 9gh - h(2e + h) + 9f*(g + h))) +
	a(9bbh(2f + h) - 3bd(6ff - 6f(3g - 2h) + g(-9g + h) + e(g + h)) +
	dd(ee + 9f(3f - g) + e(-9f - 9g + 2h))) -
	9cc(de(e + 2g) + 3b(fh + e(f + h)) + a(-3ff - 6fh + 2(gh + e(g + h)))) +
	3c(dde(e + 2f) + aa(3gg + 6gh - 2h(2f + h)) + 9bb(gh + e(g + h)) +
	ad(-9ff - 18fg + 6gg + fh + e(f + 12*g + h)) +
	b(d(-3ee + 9fg + e(9f + 9g - 6h)) + 3a(h(2e - 3g + h) - 3f(g + h)))))y

	- 3(18ccce - 18ccde + 6cdde - ddde + 3cddf - 9ccdg + aaah + 9ccc*h -
	9bbb(e + 2h) - aa(d(e - 9f + 18g - 7h) + 3c(2f - 6*g + h)) +
	a(-9cc(2e - 6f + 2g - h) + dd(-7e + 18f - 9g + h) + 3cd(7e - 17f + 3g + h)) +
	9bb(3c(e + g + h) + a(f + 2h) - d(e - 2(f - 3g + h))) -
	3b(-(dd(e - 6f + 2g)) - 3cd(e + 3f + 3g - h) + 9cc(e + f + h) + aa(g + 2*h) +
	a(c(-3e + 9f + 9g + 3h) + d(e + 3f - 17g + 7h))))*Power(y,2)

	+ Power(a - 3b + 3c - d,3)*Power(y,3)

	+ Power(x,2)(-3(-9beff + 9afff + 6beeg - 9aefg + 27befg - 27affg + 18aegg - 54begg +
	27afgg + 27bfgg - 18aggg + aeeh - 9beeh + 3aefh + 9befh + 9aff*h -
	18bffh - 21aegh + 51begh - 9afgh - 27bfgh + 18aggh + 7aehh - 18behh - 3afhh +
	18bfhh - 6aghh - 3bghh + ahh*h +
	3c(-9ff(g - 2h) + 3ggh - fh(9g + 2h) + ee(f - 6g + 6*h) +
	e(9fg + 6gg - 17fh - 3gh + 3h*h)) -
	d(eee + ee(-6f - 3g + 7h) - 9(2f - g)(ff + gg - f(g + h)) +
	e(18ff + 9gg + 3gh + hh - 3f(3g + 7h)))) )

	+ Power(x,2)(3(a - 3b + 3c - d)Power(e - 3f + 3g - h,2)y)

	+ x(-3(27bbegg - 27abfgg + 9aaggg - 18bbefh + 18abffh + 3abegh -
	27bbegh - 9aafgh + 27abfgh - 9aaggh + aaehh - 9abeh*h +
	27bbehh + 6aafhh - 18abfhh - 9bbfhh + 3aagh*h +
	6abghh - aahhh + 9cc(ee(g - 3h) - 3ffh + e(3f + 2g)h) +
	dd(eee - 9fff + 9ef(f + g) - ee(3f + 6g + h)) +
	d(-3c(-9ffg + ee(2f - 6g - 3h) + e(9fg + 6gg + f*h)) +
	a(-18fff - 18egg + 18ggg - 2eeh + 3egh + 2ehh + 9ff(3g + 2h) +
	3f(6eg - 9gg - eh - 6gh)) - 3b(9fgg + ee(4g - 3h) - 6ff*h -
	e(6ff + g(18g + h) - 3f(3g + 4*h)))) +
	3c(3b(eeh + 3fgh - e(3fg - 6fh + 6gh + h*h)) +
	a(9ff(g - 2h) + fh(-e + 9g + 4h) - 3(2ggh + e(2gg - 4gh + h*h))))) )

	+ x3(-2adee - 7ddee + 15adef + 21ddef - 9adff - 18ddff - 15adeg -
	3ddeg - 9aafg + 9ddfg + 18aagg + 9adgg + 2aaeh - 2ddeh +
	3aafh + 15adfh - 21aagh - 15adgh + 7aahh + 2adhh -
	9cc(2ee + 3ff + 3fh - 2gh + e(-3f - 4g + h)) +
	9bb(3gg - 3gh + 2h(-2f + h) + e(-2f + 3*g + h)) +
	3b(3c(ee + 3e(f - 3g) + (9f - 3g - h)h) + a(6ff + eg - 9fg - 9gg - 5eh + 9fh + 14gh - 7h*h) +
	d(-ee + 12ff - 27fg + e(-9f + 20g - 5h) + g(9g + h))) +
	3c(a(-(ef) - 9ff + 27fg - 12gg + 5eh - 20fh + 9gh + h*h) +
	d(7ee + 9ff + 9fg - 6gg - fh + e(-14f - 9g + 5h))))*y

	- x3Power(a - 3b + 3c - d,2)(e - 3f + 3g - h)Power(y,2)

	*/

	const int factors = 8;

	struct coeff {
	int s; // constant and coefficient sign
	int n[factors]; // 0 or power of a (1, 2, or 3) for a through h
	};

	enum {
	xxx_coeff,
	xxy_coeff,
	xyy_coeff,
	yyy_coeff,
	xx_coeff,
	xy_coeff,
	yy_coeff,
	x_coeff,
	y_coeff,
	c_coeff,
	coeff_count
	};

	typedef std::vector<coeff> coeffs;
	typedef std::vector<coeffs> n_coeffs;

	static char skipSpace(const char* str, size_t& index) {
	do {
	++index;
	} while (str[index] == ' ');
	return str[index];
	}

	static char backSkipSpace(const char* str, size_t& end) {
	while (str[end - 1] == ' ') {
	--end;
	}
	return str[end - 1];
	}

	static void match(const char* str, size_t len, coeffs& co, const char pattern[]) {
	size_t patternLen = strlen(pattern);
	size_t index = 0;
	while (index < len) {
	char ch = str[index];
	if (ch != '-' && ch != '+') {
	printf("missing sign\n");
	}
	size_t end = index + 1;
	while (str[end] != '+' && str[end] != '-' && ++end < len) {
	;
	}
	backSkipSpace(str, end);
	size_t idx = index;
	index = end;
	skipSpace(str, index);
	if (!strncmp(&str[end - patternLen], pattern, patternLen) == 0) {
	continue;
	}
	size_t endCoeff = end - patternLen;
	char last = backSkipSpace(str, endCoeff);
	if (last == '2' \|\| last == '3') {
	last = str[endCoeff - 3]; // skip ^2
	}
	if (last == 'x' \|\| last == 'y') {
	continue;
	}
	coeff c;
	c.s = str[idx] == '-' ? -1 : 1;
	bzero(c.n, sizeof(c.n));
	ch = skipSpace(str, idx);
	if (ch >= '2' && ch <= '6') {
	c.s *= ch - '0';
	ch = skipSpace(str, idx);
	}
	while (idx < endCoeff) {
	char x = str[idx];
	if (x < 'a' \|\| x > 'a' + factors) {
	printf("expected factor\n");
	}
	idx++;
	int pow = 1;
	if (str[idx] == '^') {
	idx++;
	char exp = str[idx];
	if (exp < '2' \|\| exp > '3') {
	printf("expected exponent\n");
	}
	pow = exp - '0';
	}
	skipSpace(str, idx);
	c.n[x - 'a'] = pow;
	}
	co.push_back(c);
	}
	}

	void cubecode_test(int test);

	void cubecode_test(int test) {
	const char* str = test ? result2 : result1;
	size_t len = strlen(str);
	n_coeffs c(coeff_count);
	match(str, len, c[xxx_coeff], "x^3"); // 1 factor
	match(str, len, c[xxy_coeff], "x^2 y"); // 1 factor
	match(str, len, c[xyy_coeff], "x y^2"); // 1 factor
	match(str, len, c[yyy_coeff], "y^3"); // 1 factor
	match(str, len, c[xx_coeff], "x^2"); // 7 factors
	match(str, len, c[xy_coeff], "x y"); // 8 factors
	match(str, len, c[yy_coeff], "y^2"); // 7 factors
	match(str, len, c[x_coeff], "x"); // 21 factors
	match(str, len, c[y_coeff], "y"); // 21 factors
	match(str, len, c[c_coeff], ""); // 34 factors : total 102
	#define COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS 0
	#define WRITE_AS_NONOPTIMIZED_C_CODE 0
	#if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
	int count[factors][factors][factors];
	bzero(count, sizeof(count));
	#endif
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf("// start of generated code");
	#endif
	for (n_coeffs::iterator it = c.begin(); it < c.end(); ++it) {
	coeffs& co = *it;
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf("\nstatic double calc_%c(double a, double b, double c, double d,"
	"\n double e, double f, double g, double h) {"
	"\n return"
	"\n ", 'A' + (it - c.begin()));
	if (co[0].s > 0) {
	printf(" ");
	}
	if (abs(co[0].s) == 1) {
	printf(" ");
	}
	#endif
	for (coeffs::iterator ct = co.begin(); ct < co.end(); ++ct) {
	const coeff& cf = *ct;
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf(" ");
	bool firstFactor = false;
	if (ct - co.begin() > 0 \|\| cf.s < 0) {
	printf("%c", cf.s < 0 ? '-' : '+');
	}
	if (ct - co.begin() > 0) {
	printf(" ");
	}
	if (abs(cf.s) > 1) {
	printf("%d * ", abs(cf.s));
	} else {
	if (ct - co.begin() > 0) {
	printf(" ");
	}
	}
	#endif
	for (int x = 0; x < factors; ++x) {
	if (cf.n[x] == 0) {
	continue;
	}
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	for (int y = 0 ; y < cf.n[x]; ++y) {
	if (y > 0 \|\| firstFactor) {
	printf(" * ");
	}
	printf("%c", 'a' + x);
	}
	firstFactor = true;
	#endif
	#if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
	for (int y = x; y < factors; ++y) {
	if (cf.n[y] == 0) {
	continue;
	}
	if (x == y && cf.n[y] == 1) {
	continue;
	}
	for (int z = y; z < factors; ++z) {
	if (cf.n[z] == 0) {
	continue;
	}
	if ((x == z \|\| y == z) && cf.n[z] == 1) {
	continue;
	}
	if (x == y && y == z && cf.n[z] == 2) {
	continue;
	}
	count[x][y][z]++;
	}
	}
	#endif
	}
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	if (ct + 1 < co.end()) {
	printf("\n");
	}
	#endif
	}
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf(";\n}\n");
	#endif
	}
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf("// end of generated code\n");
	#endif
	#if COMPUTE_MOST_FREQUENT_EXPRESSION_TRIPLETS
	const int bestCount = 20;
	int best[bestCount][4];
	bzero(best, sizeof(best));
	for (int x = 0; x < factors; ++x) {
	for (int y = x; y < factors; ++y) {
	for (int z = y; z < factors; ++z) {
	if (!count[x][y][z]) {
	continue;
	}
	for (int w = 0; w < bestCount; ++w) {
	if (best[w][0] < count[x][y][z]) {
	best[w][0] = count[x][y][z];
	best[w][1] = x;
	best[w][2] = y;
	best[w][3] = z;
	break;
	}
	}
	}
	}
	}
	for (int w = 0; w < bestCount; ++w) {
	printf("%c%c%c=%d\n", 'a' + best[w][1], 'a' + best[w][2],
	'a' + best[w][3], best[w][0]);
	}
	#endif
	#if WRITE_AS_NONOPTIMIZED_C_CODE
	printf("\n");
	#endif
	}

	/* results: variable triplets used 10 or more times:
	aah=14
	ade=14
	aeh=14
	dee=14
	bce=13
	beg=13
	beh=12
	bbe=11
	bef=11
	cee=11
	cef=11
	def=11
	ceh=10
	deg=10
	*/