# 2016q3 Homework1 (raytracing)

###### tags: `HahaSula`

---
先來按表操課

sula@sula-IdeaPad-U430p:~/workspace/raytracing$ gprof ./raytracing | less

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 24.01      0.66     0.66 56956357     0.00     0.00  subtract_vector
 20.74      1.23     0.57 69646433     0.00     0.00  dot_product
  8.73      1.47     0.24 31410180     0.00     0.00  multiply_vector
  8.37      1.70     0.23 13861875     0.00     0.00  rayRectangularIntersection
  8.00      1.92     0.22 10598450     0.00     0.00  normalize
  5.82      2.08     0.16 17821809     0.00     0.00  cross_product
  5.64      2.24     0.16 17836094     0.00     0.00  add_vector
  5.09      2.38     0.14  4620625     0.00     0.00  ray_hit_object
  4.00      2.49     0.11 13861875     0.00     0.00  raySphereIntersection
  2.55      2.56     0.07  1048576     0.00     0.00  ray_color
  1.46      2.60     0.04  4221152     0.00     0.00  multiply_vectors
  1.46      2.64     0.04        1     0.04     2.75  raytracing
  0.91      2.66     0.03  2110576     0.00     0.00  compute_specular_diffuse
  0.91      2.69     0.03  2110576     0.00     0.00  localColor
  0.73      2.71     0.02  1241598     0.00     0.00  refraction
  0.36      2.72     0.01  2520791     0.00     0.00  idx_stack_top
  0.36      2.73     0.01  1241598     0.00     0.00  protect_color_overflow
  0.36      2.74     0.01  1241598     0.00     0.00  reflection
  0.36      2.75     0.01  1048576     0.00     0.00  rayConstruction
  0.18      2.75     0.01  3838091     0.00     0.00  length

於是從計算時間最多的下手

loop unrolling
---

//math-toolkit.h
//before
//
//static inline
double dot_product(const double *v1, const double *v2)
{
    double dp = 0.0;
    for (int i = 0; i < 3; i++)
        dp += v1[i] * v2[i];
    return dp;
}
//after
static inline
double dot_product(const double *v1, const double *v2)
{
    double dp = 0.0;
    //for (int i = 0; i < 3; i++)
    //    dp += v1[i] * v2[i];
	dp = v1[0] * v2[0] + v1[1] * v2[1] + v1[2] * v2[2] ;   
	
	return dp;
}

執行時間 0.57>>>0.26(應該多做幾次做統計比較好)

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 21.41      0.43     0.43 56956357     0.00     0.00  subtract_vector
 12.94      0.69     0.26 69646433     0.00     0.00  dot_product
 

接著來對subtract_vector,multiply_vector,add_vector,multiply_vector下手看看

static inline
void subtract_vector(const double *a, const double *b, double *out)
{
	out[0] = a[0] - b[0] ;
	out[1] = a[1] - b[1] ;
	out[2] = a[2] - b[2] ;
    //for (int i = 0; i < 3; i++)
    //    out[i] = a[i] - b[i];
}

static inline
void add_vector(const double *a, const double *b, double *out)
{
	out[0] = a[0] + b[0] ;
	out[1] = a[1] + b[1] ;
	out[2] = a[2] + b[2] ;
    //for (int i = 0; i < 3; i++)
    //    out[i] = a[i] + b[i];
}

static inline
void subtract_vector(const double *a, const double *b, double *out)
{
	out[0] = a[0] - b[0] ;
	out[1] = a[1] - b[1] ;
	out[2] = a[2] - b[2] ;
    //for (int i = 0; i < 3; i++)
    //    out[i] = a[i] - b[i];
}

static inline
void multiply_vectors(const double *a, const double *b, double *out)
{
	out[0] = a[0] * b[0];
	out[1] = a[1] * b[1];
	out[2] = a[2] * b[2];
    //for (int i = 0; i < 3; i++)
    //    out[i] = a[i] * b[i];
}

static inline
void multiply_vector(const double *a, double b, double *out)
{
	out[0] = a[0] * b;
	out[1] = a[1] * b;
	out[2] = a[2] * b;
    //for (int i = 0; i < 3; i++)
    //    out[i] = a[i] * b;
}

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 15.14      0.23     0.23 69646433     0.00     0.00  dot_product
 13.17      0.43     0.20 56956357     0.00     0.00  subtract_vector
 11.19      0.60     0.17 10598450     0.00     0.00  normalize
  9.22      0.74     0.14  4620625     0.00     0.00  ray_hit_object
  7.90      0.86     0.12 13861875     0.00     0.00  raySphereIntersection
  7.24      0.97     0.11 13861875     0.00     0.00  rayRectangularIntersection
  6.25      1.07     0.10 17821809     0.00     0.00  cross_product
  4.61      1.14     0.07        1     0.07     1.51  raytracing
  4.28      1.20     0.07  4221152     0.00     0.00  multiply_vectors
  3.95      1.26     0.06 31410180     0.00     0.00  multiply_vector