Fix constant folding of division and reminder with zero divisor

Previously constant folding of zero division (e.x. 1/0) produces a
compile error. This was incorrectly implemented by checking if the
division result is infinite, so produces wrong results compared to the
query where no constant folding is processed (e.x. 1e308/0.1). This
patch delays the operation when the divisor is zero. This makes the
results more consistent, but changes the exit code on zero division from
3 to 5. Also 0/0 now produces the zero division error, not NaN.

This patch also fixes the modulo operation. Previously constant folding
logic does not take care of the % operator, but now it folds if the both
dividend and divisor are safe numbers to cast to the integer type, and
the divisor is not zero. This patch also fixes some code that relies on
undefined cast behaviors in C. The modulo operation produces NaN if
either the dividend or divisor is NaN.

2 files changed, 52 insertions, 25 deletions

diff --git a/tests/jq.test b/tests/jq.test
index 55630a5a..73cf93d0 100644
--- a/tests/jq.test
+++ b/tests/jq.test
@@ -556,9 +556,13 @@ null
 null
 172
 
-[(infinite, -infinite) % (1, -1)]
+[(infinite, -infinite) % (1, -1, infinite)]
 null
-[0,0,0,0]
+[0,0,0,0,0,-1]
+
+[nan % 1, 1 % nan | isnan]
+null
+[true,true]
 
 1 + tonumber + ("10" | tonumber)
 4
@@ -1664,18 +1668,21 @@ try (1/.) catch .
 0
 "number (1) and number (0) cannot be divided because the divisor is zero"
 
-0/0, (0 as $x | $x/0) | isnan
+try (1/0) catch .
 0
-true
-true
+"number (1) and number (0) cannot be divided because the divisor is zero"
+
+try (0/0) catch .
+0
+"number (0) and number (0) cannot be divided because the divisor is zero"
 
 try (1%.) catch .
 0
 "number (1) and number (0) cannot be divided (remainder) because the divisor is zero"
 
-%%FAIL
-1/0
-jq: error: Division by zero? at <top-level>, line 1:
+try (1%0) catch .
+0
+"number (1) and number (0) cannot be divided (remainder) because the divisor is zero"
 
 # Basic numbers tests: integers, powers of two
 [range(-52;52;1)] as $powers | [$powers[]|pow(2;.)|log2|round] == $powers
diff --git a/tests/shtest b/tests/shtest
index a644b574..3ed22c30 100755
--- a/tests/shtest
+++ b/tests/shtest
@@ -30,47 +30,67 @@ $VALGRIND $Q $JQ -Rne '[inputs] == ["a\u0000b", "c\u0000d", "e"]' $d/input
 
 # String constant folding (addition only)
 nref=$($VALGRIND $Q $JQ -n --debug-dump-disasm '"foo"' | wc -l)
+n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '"foo" + "bar"' | wc -l)
+if [ $n -ne $nref ]; then
+  echo "Constant expression folding for strings didn't work"
+  exit 1
+fi
 
-# Numeric constant folding (not all ops yet)
+# Numeric constant folding (binary operators)
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '1+1' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '1-1' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '2*3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9/3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
+fi
+n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9%3' | wc -l)
+if [ $n -ne $nref ]; then
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9==3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9!=3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
+fi
+n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9<3' | wc -l)
+if [ $n -ne $nref ]; then
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
+fi
+n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9>3' | wc -l)
+if [ $n -ne $nref ]; then
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9<=3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 n=$($VALGRIND $Q $JQ -n --debug-dump-disasm '9>=3' | wc -l)
 if [ $n -ne $nref ]; then
-    echo "Constant expression folding for strings didn't work"
-    exit 1
+  echo "Constant expression folding for numbers didn't work"
+  exit 1
 fi
 
 ## Test JSON sequence support