Fix #5931

Fix #5931 and add test case for it.

3 files changed, 31 insertions, 19 deletions

diff --git a/core/math/big/internal.odin b/core/math/big/internal.odin
index e22ea0ec7..b3e23da8c 100644
--- a/core/math/big/internal.odin
+++ b/core/math/big/internal.odin
@@ -746,19 +746,15 @@ internal_int_divmod :: proc(quotient, remainder, numerator, denominator: ^Int, a
 
 	if (denominator.used > 2 * MUL_KARATSUBA_CUTOFF) && (denominator.used <= (numerator.used / 3) * 2) {
 		assert(denominator.used >= 160 && numerator.used >= 240, "MUL_KARATSUBA_CUTOFF global not properly set.")
-		err = _private_int_div_recursive(quotient, remainder, numerator, denominator)
+		return _private_int_div_recursive(quotient, remainder, numerator, denominator)
 	} else {
-		when true {
-			err = #force_inline _private_int_div_school(quotient, remainder, numerator, denominator)
-		} else {
-			/*
-				NOTE(Jeroen): We no longer need or use `_private_int_div_small`.
-				We'll keep it around for a bit until we're reasonably certain div_school is bug free.
-			*/
-			err = _private_int_div_small(quotient, remainder, numerator, denominator)
-		}
+		return #force_inline _private_int_div_school(quotient, remainder, numerator, denominator)
+		/*
+			NOTE(Jeroen): We no longer need or use `_private_int_div_small`.
+			We'll keep it around for a bit until we're reasonably certain div_school is bug free.
+		*/
+		// err = _private_int_div_small(quotient, remainder, numerator, denominator)
 	}
-	return
 }
 
 /*
diff --git a/core/math/big/private.odin b/core/math/big/private.odin
index fb517f0b7..4847b0074 100644
--- a/core/math/big/private.odin
+++ b/core/math/big/private.odin
@@ -1050,7 +1050,6 @@ _private_int_div_school :: proc(quotient, remainder, numerator, denominator: ^In
 		Normalize both x and y, ensure that y >= b/2, [b == 2**MP_DIGIT_BIT]
 	*/
 	norm := internal_count_bits(y) % _DIGIT_BITS
-
 	if norm < _DIGIT_BITS - 1 {
 		norm = (_DIGIT_BITS - 1) - norm
 		internal_shl(x, x, norm) or_return
@@ -1070,33 +1069,29 @@ _private_int_div_school :: proc(quotient, remainder, numerator, denominator: ^In
 		y = y*b**{n-t}
 	*/
 
+
 	_private_int_shl_leg(y, n - t) or_return
 
-	gte := internal_gte(x, y)
-	for gte {
+	for internal_gte(x, y) {
 		q.digit[n - t] += 1
 		internal_sub(x, x, y) or_return
-		gte = internal_gte(x, y)
 	}
 
 	/*
 		Reset y by shifting it back down.
 	*/
 	_private_int_shr_leg(y, n - t)
-
 	/*
 		Step 3. for i from n down to (t + 1).
 	*/
 	#no_bounds_check for i := n; i >= (t + 1); i -= 1 {
 		if i > x.used { continue }
-
 		/*
 			step 3.1 if xi == yt then set q{i-t-1} to b-1, otherwise set q{i-t-1} to (xi*b + x{i-1})/yt
 		*/
 		if x.digit[i] == y.digit[t] {
-			q.digit[(i - t) - 1] = 1 << (_DIGIT_BITS - 1)
+			q.digit[(i - t) - 1] = 1 << _DIGIT_BITS - 1
 		} else {
-
 			tmp := _WORD(x.digit[i]) << _DIGIT_BITS
 			tmp |= _WORD(x.digit[i - 1])
 			tmp /= _WORD(y.digit[t])
diff --git a/tests/core/math/big/test_core_math_big.odin b/tests/core/math/big/test_core_math_big.odin
index 42df7154f..766ff78b0 100644
--- a/tests/core/math/big/test_core_math_big.odin
+++ b/tests/core/math/big/test_core_math_big.odin
@@ -224,6 +224,27 @@ test_big_math_vectors :: proc(t: ^testing.T) {
 	}
 }
 
+@(test)
+bug_5931 :: proc(t: ^testing.T) {
+	numerator, divisor, quotient, remainder: big.Int
+	defer big.destroy(&numerator, &divisor, &quotient, &remainder)
+
+	big.string_to_int(&numerator, "3351951982485649274893506249551461531869841455148098344430890360930192345844485855956241793418914802713278852793799976230545127411560969441984014513833901")
+	big.string_to_int(&divisor,   "115792089237316195423570985008687907853269984665640564039457584007908834671663")
+
+	big.int_divmod(&quotient, &remainder, &numerator, &divisor)
+	quo_str, _ := big.int_itoa_string(&quotient)
+	defer delete(quo_str)
+	assert(quo_str == "28948022309329048855892746252171976963317496166410141009864396001977208667923")
+
+	rem_str, _ := big.int_itoa_string(&remainder)
+	defer delete(rem_str)
+	assert(rem_str == "28948022309329048855892746252171976963317496166410141009864396001977208667952")
+}
+
+
+// Test helpers
+
 expect_a :: proc(t: ^testing.T, format: string, a, expected, res: ^big.Int, err: big.Error, loc := #caller_location) {
 	if err != .Okay { return }