From 92a5425aaa49d90d4d4c1e88e8595ce932c1ad9b Mon Sep 17 00:00:00 2001
From: tlatorre <tlatorre@uchicago.edu>
Date: Mon, 29 Jul 2019 12:23:30 -0500
Subject: fast_sqrt -> sqrt

After some testing, I realized that the fast_sqrt() function wasn't really
faster than the native sqrt function.
---
 src/likelihood.c |  4 ++--
 src/misc.c       | 22 ----------------------
 src/misc.h       |  4 ----
 src/test.c       | 27 ---------------------------
 4 files changed, 2 insertions(+), 55 deletions(-)

(limited to 'src')

diff --git a/src/likelihood.c b/src/likelihood.c
index 9037cb9..abf064f 100644
--- a/src/likelihood.c
+++ b/src/likelihood.c
@@ -572,10 +572,10 @@ static void get_expected_charge(double beta, double theta0, double *pos, double
     /* Calculate the cosine of the angle between the track direction and the
      * vector to the PMT. */
     cos_theta = DOT(dir,pmt_dir);
-    sin_theta = fast_sqrt(1-cos_theta*cos_theta);
+    sin_theta = sqrt(1-cos_theta*cos_theta);
 
     cos_theta_pmt = -DOT(pmt_dir,pmts[pmt].normal);
-    sin_theta_pmt = fast_sqrt(1-cos_theta_pmt*cos_theta_pmt);
+    sin_theta_pmt = sqrt(1-cos_theta_pmt*cos_theta_pmt);
 
     theta0 = fmax(theta0,get_theta0_min(distance_to_pmt,PMT_RADIUS,sin_theta_pmt));
 
diff --git a/src/misc.c b/src/misc.c
index 003b170..f705c74 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -881,25 +881,3 @@ double fast_acos(double x)
 
     return interp1d(x,xs,ys,LEN(xs));
 }
-
-/* Fast version of sqrt() for `x` between 0 and 1 which uses a lookup table
- * computed on the first call. */
-double fast_sqrt(double x)
-{
-    size_t i;
-    static int initialized = 0;
-    static double xs[N_SQRT];
-    static double ys[N_SQRT];
-
-    if (!initialized) {
-        for (i = 0; i < LEN(xs); i++) {
-            xs[i] = 1.0*i/(LEN(xs)-1);
-            ys[i] = sqrt(xs[i]);
-        }
-        initialized = 1;
-    }
-
-    if (x > 1.0) return sqrt(x);
-
-    return interp1d(x,xs,ys,LEN(xs));
-}
diff --git a/src/misc.h b/src/misc.h
index e40c1f5..60e54ea 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -30,9 +30,6 @@
 /* Number of points to create a lookup table for the fast_acos() function. */
 #define N_ACOS 10000
 
-/* Number of points to create a lookup table for the fast_sqrt() function. */
-#define N_SQRT 10000
-
 double trapz(const double *y, double dx, size_t n);
 int intersect_sphere(double *pos, double *dir, double R, double *l);
 void get_path_length(double *pos1, double *pos2, double R, double *l1, double *l2);
@@ -58,6 +55,5 @@ size_t argmax(double *a, size_t n);
 size_t argmin(double *a, size_t n);
 void get_dir(double *dir, double theta, double phi);
 double fast_acos(double x);
-double fast_sqrt(double x);
 
 #endif
diff --git a/src/test.c b/src/test.c
index 100091c..d07ee11 100644
--- a/src/test.c
+++ b/src/test.c
@@ -2100,32 +2100,6 @@ err:
     return 1;
 }
 
-int test_fast_sqrt(char *err)
-{
-    /* Tests that the fast_sqrt() function returns values within 0.1% of sqrt(). */
-    size_t i;
-    double x, result, expected;
-
-    init_genrand(0);
-
-    for (i = 0; i < 100; i++) {
-        x = genrand_real2()*2;
-
-        result = fast_sqrt(x);
-        expected = sqrt(x);
-
-        if (!isclose(result, expected, 0, 1e-3)) {
-            sprintf(err, "fast_sqrt() returned %.5g, but expected %.5g", result, expected);
-            goto err;
-        }
-    }
-
-    return 0;
-
-err:
-    return 1;
-}
-
 int test_get_most_likely_mean_pe(char *err)
 {
     /* Tests that the get_most_likely_mean_pe() function returns values which
@@ -2207,7 +2181,6 @@ struct tests {
     {test_argmin, "test_argmin"},
     {test_electron_get_angular_pdf_norm, "test_electron_get_angular_pdf_norm"},
     {test_fast_acos, "test_fast_acos"},
-    {test_fast_sqrt, "test_fast_sqrt"},
     {test_get_most_likely_mean_pe, "test_get_most_likely_mean_pe"},
 };
 
-- 
cgit