refactor: move bsearch function to C-code (#2945)

This commit fixes issue #527 and move the bsearch function to a native
C-code. This change improves the performance of this function.

src/builtin.c

@@ -835,6 +835,40 @@ static jv f_sort_by_impl(jq_state *jq, jv input, jv keys) {
   }
 }
 
+/*
+ * Assuming the input array is sorted, bsearch/1 returns
+ * the index of the target if the target is in the input array; and otherwise
+ * (-1 - ix), where ix is the insertion point that would leave the array sorted.
+ * If the input is not sorted, bsearch will terminate but with irrelevant results.
+ */
+static jv f_bsearch(jq_state *jq, jv input, jv target) {
+  if (jv_get_kind(input) != JV_KIND_ARRAY) {
+    jv_free(target);
+    return type_error(input, "cannot be searched from");
+  }
+  int start = 0;
+  int end = jv_array_length(jv_copy(input));
+  jv answer = jv_invalid();
+  while (start < end) {
+    int mid = start + (end - start) / 2;
+    int result = jv_cmp(jv_copy(target), jv_array_get(jv_copy(input), mid));
+    if (result == 0) {
+      answer = jv_number(mid);
+      break;
+    } else if (result < 0) {
+      end = mid;
+    } else {
+      start = mid + 1;
+    }
+  }
+  if (!jv_is_valid(answer)) {
+    answer = jv_number(-1 - start);
+  }
+  jv_free(input);
+  jv_free(target);
+  return answer;
+}
+
 static jv f_group_by_impl(jq_state *jq, jv input, jv keys) {
   if (jv_get_kind(input) == JV_KIND_ARRAY &&
       jv_get_kind(keys) == JV_KIND_ARRAY &&
@@ -1844,6 +1878,7 @@ BINOPS
   CFUNC(f_sort, "sort", 1),
   CFUNC(f_sort_by_impl, "_sort_by_impl", 2),
   CFUNC(f_group_by_impl, "_group_by_impl", 2),
+  CFUNC(f_bsearch, "bsearch", 2),
   CFUNC(f_min, "min", 1),
   CFUNC(f_max, "max", 1),
   CFUNC(f_min_by_impl, "_min_by_impl", 2),

src/builtin.jq

@@ -219,37 +219,6 @@ def tostream:
   getpath($p) |
   reduce path(.[]?) as $q ([$p, .]; [$p+$q]);
 
-# Assuming the input array is sorted, bsearch/1 returns
-# the index of the target if the target is in the input array; and otherwise
-#  (-1 - ix), where ix is the insertion point that would leave the array sorted.
-# If the input is not sorted, bsearch will terminate but with irrelevant results.
-def bsearch($target):
-  if length == 0 then -1
-  elif length == 1 then
-     if $target == .[0] then 0 elif $target < .[0] then -1 else -2 end
-  else . as $in
-    # state variable: [start, end, answer]
-    # where start and end are the upper and lower offsets to use.
-    | [0, length-1, null]
-    | until( .[0] > .[1] ;
-             if .[2] != null then (.[1] = -1)               # i.e. break
-             else
-               ( ( (.[1] + .[0]) / 2 ) | floor ) as $mid
-               | $in[$mid] as $monkey
-               | if $monkey == $target  then (.[2] = $mid)   # success
-                 elif .[0] == .[1]     then (.[1] = -1)     # failure
-                 elif $monkey < $target then (.[0] = ($mid + 1))
-                 else (.[1] = ($mid - 1))
-                 end
-             end )
-    | if .[2] == null then          # compute the insertion point
-         if $in[ .[0] ] < $target then (-2 -.[0])
-         else (-1 -.[0])
-         end
-      else .[2]
-      end
-  end;
-
 # Apply f to composite entities recursively, and to atoms
 def walk(f):
   def w:

tests/jq.test

@@ -1642,12 +1642,22 @@ ascii_upcase
 "useful but not for é"
 "USEFUL BUT NOT FOR é"
 
-bsearch(0,2,4)
+bsearch(0,1,2,3,4)
 [1,2,3]
 -1
+0
 1
+2
 -4
 
+bsearch({x:1})
+[{ "x": 0 },{ "x": 1 },{ "x": 2 }]
+1
+
+try ["OK", bsearch(0)] catch ["KO",.]
+"aa"
+["KO","string (\"aa\") cannot be searched from"]
+
 # strptime tests are in optional.test
 
 strftime("%Y-%m-%dT%H:%M:%SZ")