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Reword note on wrapping arithmetic

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This commit is contained in:
Karoy Lorentey
2022-02-03 11:39:44 -08:00
committed by GitHub
parent b1683c89be
commit a3fdcfa43f
1 changed files with 10 additions and 18 deletions
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28
stdlib/public/core/UnsafeBufferPointer.swift.gyb
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@@ -143,9 +143,11 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// NOTE: Wrapping math because we allow unsafe buffer pointers not to verify
// index preconditions in release builds. Our (optimistic) assumption is
// that the caller is already ensuring that indices are valid, so we can
// elide the usual checks to help the optimizer generate better code.
// However, we still check for overflow in debug mode.
let result = i.addingReportingOverflow(1)
_debugPrecondition(!result.overflow)
return result.partialValue
@@ -158,9 +160,7 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// See note on wrapping arithmetic in `index(after:)` above.
let result = i.addingReportingOverflow(1)
_debugPrecondition(!result.overflow)
i = result.partialValue
@@ -173,9 +173,7 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// See note on wrapping arithmetic in `index(after:)` above.
let result = i.subtractingReportingOverflow(1)
_debugPrecondition(!result.overflow)
return result.partialValue
@@ -188,9 +186,7 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// See note on wrapping arithmetic in `index(after:)` above.
let result = i.subtractingReportingOverflow(1)
_debugPrecondition(!result.overflow)
i = result.partialValue
@@ -203,9 +199,7 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// See note on wrapping arithmetic in `index(after:)` above.
let result = i.addingReportingOverflow(n)
_debugPrecondition(!result.overflow)
return result.partialValue
@@ -218,9 +212,7 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
// optimizer is not capable of creating partial specializations yet.
// NOTE: Range checks are not performed here, because it is done later by
// the subscript function.
// NOTE: Unchecked math because unsafe pointers are not required to
// behave sensibly if you misuse their indices. We validate in
// debug mode.
// See note on wrapping arithmetic in `index(after:)` above.
let maxOffset = limit.subtractingReportingOverflow(i)
_debugPrecondition(!maxOffset.overflow)
let l = maxOffset.partialValue