added better error messages!

scratchpad/scratchpad.c

@@ -1,24 +1,19 @@
-#include <float.h> // FLT_MAX, FLT_MIN
 #include <limits.h> // INT_MAX
-#include <math.h>
 #include <stdint.h>
-#include <stdio.h>
 #include <stdlib.h>
-#define VERBOSE 1
+#include <float.h> // FLT_MAX, FLT_MIN
+#include <stdio.h>
+#include <math.h> // erf, sqrt
+
+#define EXIT_ON_ERROR 0
 
 // Errors
-// https://mccue.dev/pages/7-27-22-c-errors
-// Huh, first time I've really needed a struct
-// https://en.wikipedia.org/wiki/Struct_(C_programming_language)
-// https://www.cs.yale.edu/homes/aspnes/pinewiki/C(2f)Structs.html
-// https://stackoverflow.com/questions/9653072/return-a-struct-from-a-function-in-c
-// options:
-//   - exit
-//   - pass structs
-// to do: reuse more informative printing from build-your-own-lisp?
+// [ ] to do: reuse more informative printing from build-your-own-lisp?
+// Another option could be to exit on error. Maybe let the user decide?
 struct box {
     int empty;
     float content;
+		char * error_msg;
 };
 
 // Example cdf
@@ -48,23 +43,23 @@ float cdf_normal_0_1(float x)
 {
     float mean = 0;
     float std = 1;
-    return 0.5 * (1 + erf((x - mean) / (std * sqrt(2))));
+    return 0.5 * (1 + erf((x - mean) / (std * sqrt(2)))); // erf from math.h
 }
 
 // Inverse cdf
 struct box inverse_cdf(float cdf(float), float p)
 {
     // given a cdf: [-Inf, Inf] => [0,1]
-    // returns x such that cdf(x) = p
-    // [x] to do: add bounds, add error checking
-    // [x] maybe return a struct or smth.
+    // returns a box with either
+		// x such that cdf(x) = p
+		// or an error
+		// if EXIT_ON_ERROR is set to 1, it exits instead of providing an error
 
     struct box result;
     float low = -1.0;
     float high = 1.0;
 
     // 1. Make sure that cdf(low) < p < cdf(high)
-    // [x] to do: do smth with float min and float max?
     int interval_found = 0;
     while ((!interval_found) && (low > -FLT_MAX / 4) && (high < FLT_MAX / 4)) {
         // ^ Using FLT_MIN and FLT_MAX is overkill
@@ -80,17 +75,18 @@ struct box inverse_cdf(float cdf(float), float p)
             high = high * 2;
         }
     }
-    if (0) {
-        printf("FLT_MIN = %f, FLT_MAX = %f, INT_MAX = %d\n", -FLT_MAX, FLT_MAX, INT_MAX);
-        printf("low: %f, high: %f\n", low, high);
-        printf("interval_found? %d\n", interval_found);
-        int while_condition = (!interval_found) && (low > FLT_MIN / 4) && (high < FLT_MAX / 4);
-        printf("while condition: %i\n", while_condition);
-    }
 
 		if (!interval_found) {
+			  if(EXIT_ON_ERROR){
+					printf("Interval containing the target value not found, in function inverse_cdf, in %s (%d)", __FILE__, __LINE__);
+					exit(1);
+				}else{
+					char error_msg[200];
+					snprintf(error_msg, 200, "Interval containing the target value not found in function inverse_cdf, in %s (%d)", __FILE__, __LINE__);
 					result.empty = 1;
+					result.error_msg = error_msg;
 					return result;
+				}
     } else {
 
         int convergence_condition = 0;
@@ -123,6 +119,16 @@ struct box inverse_cdf(float cdf(float), float p)
             result.content = low;
             result.empty = 0;
         } else {
+						if(EXIT_ON_ERROR){
+							printf("Search process did not converge, in function inverse_cdf, in %s (%d)", __FILE__, __LINE__);
+							exit(1);
+						}else{
+							char error_msg[200];
+							snprintf(error_msg, 200, "Search process did not converge, in function inverse_cdf, in %s (%d)", __FILE__, __LINE__);
+							result.empty = 1;
+							result.error_msg = error_msg;
+							return result;
+						}
 								result.empty = 1;
 					}
 
@@ -146,13 +152,12 @@ uint32_t xorshift32(uint32_t* seed)
 }
 
 // Distribution & sampling functions
-
 float rand_0_to_1(uint32_t* seed)
 {
     return ((float)xorshift32(seed)) / ((float)UINT32_MAX);
 }
 
-// sampler based on inverse cdf
+// Sampler based on inverse cdf
 struct box sampler(float cdf(float), uint32_t* seed)
 {
     struct box result;
@@ -161,16 +166,15 @@ struct box sampler(float cdf(float), uint32_t* seed)
     return result;
 }
 
-// ~~[-] to-do: integrals => beta distribution~~
-// => instead, use this incomplete beta function implementation, based on continuous fractions:
+// to do: add beta. 
+// for the cdf, use this incomplete beta function implementation, based on continuous fractions:
 // <https://codeplea.com/incomplete-beta-function-c>
 // <https://github.com/codeplea/incbeta>
 
-// main with an example
 int main()
 {
 
-    // Uniform:
+    // Get the inverse cdf of a [0,1] uniform distribution at 0.5
     struct box result_1 = inverse_cdf(cdf_uniform_0_1, 0.5);
     char* name_1 = "cdf_uniform_0_1";
     if (result_1.empty) {
@@ -180,7 +184,7 @@ int main()
         printf("Inverse of %s at %f is: %f\n", name_1, 0.5, result_1.content);
     }
 
-    // Squared cdf
+    // Get the inverse cdf of a [0,1] squared distribution at 0.5
     struct box result_2 = inverse_cdf(cdf_squared_0_1, 0.5);
     char* name_2 = "cdf_squared_0_1";
     if (result_2.empty) {
@@ -190,7 +194,7 @@ int main()
         printf("Inverse of %s at %f is: %f\n", name_2, 0.5, result_2.content);
     }
 
-    // Normal cdf
+		// Get the inverse of a normal(0,1) cdf distribution
     struct box result_3 = inverse_cdf(cdf_normal_0_1, 0.5);
     char* name_3 = "cdf_normal_0_1";
     if (result_3.empty) {
@@ -200,6 +204,7 @@ int main()
         printf("Inverse of %s at %f is: %f\n", name_3, 0.5, result_3.content);
     }
 
+		// Use the sampler on a normal(0,1)
     // set randomness seed
     uint32_t* seed = malloc(sizeof(uint32_t));
     *seed = 1000; // xorshift can't start with 0