Avoid division by zero with fixed-point DIV and LOG

Rangi42 · Dec 30, 2024 · 198b6f1 · 198b6f1
1 parent afaaf0a
commit 198b6f1
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Showing 2 changed files with 12 additions and 2 deletions.
diff --git a/src/asm/fixpoint.cpp b/src/asm/fixpoint.cpp
@@ -73,7 +73,11 @@ int32_t fix_Mul(int32_t i, int32_t j, int32_t q) {
 }
 
 int32_t fix_Div(int32_t i, int32_t j, int32_t q) {
-	return double2fix(fix2double(i, q) / fix2double(j, q), q);
+	double dividend = fix2double(i, q);
+	double divisor = fix2double(j, q);
+	if (divisor == 0.0)
+		return dividend < 0 ? INT32_MIN : dividend > 0 ? INT32_MAX : 0;
+	return double2fix(dividend / divisor, q);
 }
 
 int32_t fix_Mod(int32_t i, int32_t j, int32_t q) {
@@ -85,7 +89,10 @@ int32_t fix_Pow(int32_t i, int32_t j, int32_t q) {
 }
 
 int32_t fix_Log(int32_t i, int32_t j, int32_t q) {
-	return double2fix(log(fix2double(i, q)) / log(fix2double(j, q)), q);
+	double divisor = log(fix2double(j, q));
+	if (divisor == 0.0)
+		return INT32_MAX;
+	return double2fix(log(fix2double(i, q)) / divisor, q);
 }
 
 int32_t fix_Round(int32_t i, int32_t q) {

diff --git a/test/asm/math.asm b/test/asm/math.asm
@@ -37,6 +37,9 @@ ENDM
 
 	assert LOG(100.0, 10.0) == 2.0
 	assert LOG(256.0, 2.0) == 8.0
+	assert LOG(10.0, 1.0) == $7fff_ffff ; +inf
+	assert LOG(0.0, 2.71828) == $8000_0000 ; -inf
+	assert LOG(-1.0, 2.71828) == 0 ; nan
 
 	assert ROUND(1.5) == 2.0
 	assert ROUND(-1.5) == -2.0