From c563521d44e857e2ef80885a43304f1e6c64713b Mon Sep 17 00:00:00 2001
From: Robin Voetter <robin@voetter.nl>
Date: Sun, 24 Oct 2021 02:55:23 +0200
Subject: [PATCH] big ints: tighten some more division memory requirements

---
 lib/std/math/big/int.zig | 13 ++++++-------
 src/value.zig            |  8 ++++----
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/lib/std/math/big/int.zig b/lib/std/math/big/int.zig
index 91a8d37813..3b344f89db 100644
--- a/lib/std/math/big/int.zig
+++ b/lib/std/math/big/int.zig
@@ -763,8 +763,8 @@ pub const Mutable = struct {
     /// q may alias with a or b.
     ///
     /// Asserts there is enough memory to store q and r.
-    /// The upper bound for r limb count is b.limbs.len.
-    /// The upper bound for q limb count is given by `a.limbs.len + b.limbs.len`.
+    /// The upper bound for r limb count is `b.limbs.len`.
+    /// The upper bound for q limb count is given by `a.limbs`.
     ///
     /// If `allocator` is provided, it will be used for temporary storage to improve
     /// multiplication performance. `error.OutOfMemory` is handled with a fallback algorithm.
@@ -893,9 +893,8 @@ pub const Mutable = struct {
     /// q may alias with a or b.
     ///
     /// Asserts there is enough memory to store q and r.
-    /// The upper bound for r limb count is a.limbs.len.
-    /// The upper bound for q limb count is given by `calcQuotientLimbLen`. This accounts
-    /// for temporary space used by the division algorithm.
+    /// The upper bound for r limb count is `b.limbs.len`.
+    /// The upper bound for q limb count is given by `a.limbs.len`.
     ///
     /// If `allocator` is provided, it will be used for temporary storage to improve
     /// multiplication performance. `error.OutOfMemory` is handled with a fallback algorithm.
@@ -2569,7 +2568,7 @@ pub const Managed = struct {
     ///
     /// Returns an error if memory could not be allocated.
     pub fn divFloor(q: *Managed, r: *Managed, a: Const, b: Const) !void {
-        try q.ensureCapacity(a.limbs.len + b.limbs.len);
+        try q.ensureCapacity(a.limbs.len);
         try r.ensureCapacity(b.limbs.len);
         var mq = q.toMutable();
         var mr = r.toMutable();
@@ -2586,7 +2585,7 @@ pub const Managed = struct {
     ///
     /// Returns an error if memory could not be allocated.
     pub fn divTrunc(q: *Managed, r: *Managed, a: Const, b: Const) !void {
-        try q.ensureCapacity(a.limbs.len + b.limbs.len);
+        try q.ensureCapacity(a.limbs.len);
         try r.ensureCapacity(b.limbs.len);
         var mq = q.toMutable();
         var mr = r.toMutable();
diff --git a/src/value.zig b/src/value.zig
index 15970390ba..8fe62b82b9 100644
--- a/src/value.zig
+++ b/src/value.zig
@@ -2301,7 +2301,7 @@ pub const Value = extern union {
         const rhs_bigint = rhs.toBigInt(&rhs_space);
         const limbs_q = try allocator.alloc(
             std.math.big.Limb,
-            lhs_bigint.limbs.len + rhs_bigint.limbs.len,
+            lhs_bigint.limbs.len,
         );
         const limbs_r = try allocator.alloc(
             std.math.big.Limb,
@@ -2332,7 +2332,7 @@ pub const Value = extern union {
         const rhs_bigint = rhs.toBigInt(&rhs_space);
         const limbs_q = try allocator.alloc(
             std.math.big.Limb,
-            lhs_bigint.limbs.len + rhs_bigint.limbs.len,
+            lhs_bigint.limbs.len,
         );
         const limbs_r = try allocator.alloc(
             std.math.big.Limb,
@@ -2363,7 +2363,7 @@ pub const Value = extern union {
         const rhs_bigint = rhs.toBigInt(&rhs_space);
         const limbs_q = try allocator.alloc(
             std.math.big.Limb,
-            lhs_bigint.limbs.len + rhs_bigint.limbs.len,
+            lhs_bigint.limbs.len,
         );
         const limbs_r = try allocator.alloc(
             std.math.big.Limb,
@@ -2396,7 +2396,7 @@ pub const Value = extern union {
         const rhs_bigint = rhs.toBigInt(&rhs_space);
         const limbs_q = try allocator.alloc(
             std.math.big.Limb,
-            lhs_bigint.limbs.len + rhs_bigint.limbs.len,
+            lhs_bigint.limbs.len,
         );
         const limbs_r = try allocator.alloc(
             std.math.big.Limb,