Fix division and modulo for very large negative numbers (#1790)

src/opmath.cpp

@@ -11,15 +11,16 @@
 int32_t op_divide(int32_t dividend, int32_t divisor) {
 	// Adjust division to floor toward negative infinity,
 	// not truncate toward zero
-	return dividend / divisor - ((dividend % divisor < 0) != (divisor < 0));
+	int32_t remainder = dividend % divisor;
+	return dividend / divisor - (remainder != 0 && (remainder < 0) != (divisor < 0));
 }
 
 int32_t op_modulo(int32_t dividend, int32_t divisor) {
-	int32_t remainder = dividend % divisor;
-
 	// Adjust modulo to have the sign of the divisor,
 	// not the sign of the dividend
-	return remainder + divisor * ((remainder < 0) != (divisor < 0));
+	return static_cast<int32_t>(
+	    dividend - static_cast<int64_t>(op_divide(dividend, divisor)) * divisor
+	);
 }
 
 int32_t op_exponent(int32_t base, uint32_t power) {

test/asm/div-negative.asm

@@ -0,0 +1,47 @@
+MACRO test
+	def num = \1
+	def den = \2
+	def quo = num / den
+	def rem = num % den
+	def rev = quo * den + rem
+	assert num == rev
+	println "{ 11d:num} (${08x:num}) / { 11d:den} (${08x:den}) = { 11d:quo} (${08x:quo}) R { 11d:rem} (${08x:rem})"
+ENDM
+
+test $8000_0000, $8000_0000
+test $8000_0000, $c000_0000
+test $8000_0000, $f000_0000
+test $8000_0000, $f800_0000
+test $8000_0000, $ff00_0000
+
+test $c000_0000, $8000_0000
+test $c000_0000, $c000_0000
+test $c000_0000, $f000_0000
+test $c000_0000, $f800_0000
+test $c000_0000, $ff00_0000
+
+test $f800_0000, $8000_0000
+test $f800_0000, $c000_0000
+test $f800_0000, $f000_0000
+test $f800_0000, $f800_0000
+test $f800_0000, $ff00_0000
+
+test $0000_0000, $8000_0000
+test $0000_0000, $c000_0000
+test $0000_0000, $f000_0000
+test $0000_0000, $f800_0000
+test $0000_0000, $ff00_0000
+
+test $0080_0000, $ff80_0000
+
+test $0300_0000, $fd00_0000
+test $0300_0000, $ff00_0000
+test $0300_0000, $ff80_0000
+
+test $6000_0000, $fd00_0000
+test $6000_0000, $ff00_0000
+test $6000_0000, $ff80_0000
+
+test $7f00_0000, $fd00_0000
+test $7f00_0000, $ff00_0000
+test $7f00_0000, $ff80_0000

test/asm/div-negative.out

@@ -0,0 +1,30 @@
+-2147483648 ($80000000) / -2147483648 ($80000000) =           1 ($00000001) R           0 ($00000000)
+-2147483648 ($80000000) / -1073741824 ($c0000000) =           2 ($00000002) R           0 ($00000000)
+-2147483648 ($80000000) /  -268435456 ($f0000000) =           8 ($00000008) R           0 ($00000000)
+-2147483648 ($80000000) /  -134217728 ($f8000000) =          16 ($00000010) R           0 ($00000000)
+-2147483648 ($80000000) /   -16777216 ($ff000000) =         128 ($00000080) R           0 ($00000000)
+-1073741824 ($c0000000) / -2147483648 ($80000000) =           0 ($00000000) R -1073741824 ($c0000000)
+-1073741824 ($c0000000) / -1073741824 ($c0000000) =           1 ($00000001) R           0 ($00000000)
+-1073741824 ($c0000000) /  -268435456 ($f0000000) =           4 ($00000004) R           0 ($00000000)
+-1073741824 ($c0000000) /  -134217728 ($f8000000) =           8 ($00000008) R           0 ($00000000)
+-1073741824 ($c0000000) /   -16777216 ($ff000000) =          64 ($00000040) R           0 ($00000000)
+ -134217728 ($f8000000) / -2147483648 ($80000000) =           0 ($00000000) R  -134217728 ($f8000000)
+ -134217728 ($f8000000) / -1073741824 ($c0000000) =           0 ($00000000) R  -134217728 ($f8000000)
+ -134217728 ($f8000000) /  -268435456 ($f0000000) =           0 ($00000000) R  -134217728 ($f8000000)
+ -134217728 ($f8000000) /  -134217728 ($f8000000) =           1 ($00000001) R           0 ($00000000)
+ -134217728 ($f8000000) /   -16777216 ($ff000000) =           8 ($00000008) R           0 ($00000000)
+          0 ($00000000) / -2147483648 ($80000000) =           0 ($00000000) R           0 ($00000000)
+          0 ($00000000) / -1073741824 ($c0000000) =           0 ($00000000) R           0 ($00000000)
+          0 ($00000000) /  -268435456 ($f0000000) =           0 ($00000000) R           0 ($00000000)
+          0 ($00000000) /  -134217728 ($f8000000) =           0 ($00000000) R           0 ($00000000)
+          0 ($00000000) /   -16777216 ($ff000000) =           0 ($00000000) R           0 ($00000000)
+    8388608 ($00800000) /    -8388608 ($ff800000) =          -1 ($ffffffff) R           0 ($00000000)
+   50331648 ($03000000) /   -50331648 ($fd000000) =          -1 ($ffffffff) R           0 ($00000000)
+   50331648 ($03000000) /   -16777216 ($ff000000) =          -3 ($fffffffd) R           0 ($00000000)
+   50331648 ($03000000) /    -8388608 ($ff800000) =          -6 ($fffffffa) R           0 ($00000000)
+ 1610612736 ($60000000) /   -50331648 ($fd000000) =         -32 ($ffffffe0) R           0 ($00000000)
+ 1610612736 ($60000000) /   -16777216 ($ff000000) =         -96 ($ffffffa0) R           0 ($00000000)
+ 1610612736 ($60000000) /    -8388608 ($ff800000) =        -192 ($ffffff40) R           0 ($00000000)
+ 2130706432 ($7f000000) /   -50331648 ($fd000000) =         -43 ($ffffffd5) R   -33554432 ($fe000000)
+ 2130706432 ($7f000000) /   -16777216 ($ff000000) =        -127 ($ffffff81) R           0 ($00000000)
+ 2130706432 ($7f000000) /    -8388608 ($ff800000) =        -254 ($ffffff02) R           0 ($00000000)

test/link/patch-diagnostics.asm

@@ -1,6 +1,7 @@
 def fzero equs "startof(\"test\")"
 section "test", rom0
 ld a, $8000_0000 / (fzero - 1)
+ld a, $8000_0000 / (fzero - 2)
 ld a, 1 << (fzero - 1)
 ld a, 1 << (fzero + 32)
 ld a, (fzero - 1) >> 1

test/link/patch-diagnostics.out

@@ -1,16 +1,18 @@
 warning: Shifting right by large amount 32 [-Wshift-amount]
+    at patch-diagnostics.asm(11)
+warning: Shifting right by negative amount -1 [-Wshift-amount]
     at patch-diagnostics.asm(10)
-warning: Shifting right by negative amount -1 [-Wshift-amount]
-    at patch-diagnostics.asm(9)
 warning: Shifting right by large amount 32 [-Wshift-amount]
-    at patch-diagnostics.asm(8)
+    at patch-diagnostics.asm(9)
 warning: Shifting right by negative amount -1 [-Wshift-amount]
-    at patch-diagnostics.asm(7)
+    at patch-diagnostics.asm(8)
 warning: Shifting right negative value -1 [-Wshift]
-    at patch-diagnostics.asm(6)
+    at patch-diagnostics.asm(7)
 warning: Shifting left by large amount 32 [-Wshift-amount]
-    at patch-diagnostics.asm(5)
+    at patch-diagnostics.asm(6)
 warning: Shifting left by negative amount -1 [-Wshift-amount]
+    at patch-diagnostics.asm(5)
+warning: Value $40000000 is not 8-bit [-Wtruncation]
     at patch-diagnostics.asm(4)
 warning: Division of -2147483648 by -1 yields -2147483648 [-Wdiv]
     at patch-diagnostics.asm(3)