OverflowSemantics.cpp

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//===-- OverflowSemantics.cpp - Cast overflow helpers -----------*- C++ -*-===//
//
// Part of the LLZK Project, under the Apache License v2.0.
// See LICENSE.txt for license information.
// Copyright 2026 Project LLZK
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
 
#include "llzk/Dialect/Cast/Util/OverflowSemantics.h"
 
#include <llvm/Support/ErrorHandling.h>
 
using namespace llvm;
 
namespace llzk::cast {
namespace {
 
static DynamicAPInt positiveModulo(const DynamicAPInt &value, const DynamicAPInt &modulus) {
  DynamicAPInt result = value % modulus;
  return result < 0 ? result + modulus : result;
}
 
} // namespace
 
std::optional<DynamicAPInt>
applyIntToFeltOverflow(const DynamicAPInt &value, const Field &field, OverflowSemantics overflow) {
  switch (overflow) {
  case OverflowSemantics::ASSERT:
    return value < 0 || value >= field.prime() ? std::nullopt : std::optional(value);
  case OverflowSemantics::SATURATE:
    return value < 0 ? field.zero() : (value < field.maxVal() ? value : field.maxVal());
  case OverflowSemantics::WRAP:
    return field.reduce(value);
  case OverflowSemantics::TRUNCATE:
    return field.reduce(positiveModulo(value, DynamicAPInt(1) << field.bitWidth()));
  }
  llvm_unreachable("unknown overflow semantics");
}
 
std::optional<DynamicAPInt> applyFeltToIndexOverflow(
    const DynamicAPInt &value, unsigned indexBitWidth, OverflowSemantics overflow
) {
  const DynamicAPInt safeUpperBound = (DynamicAPInt(1) << (indexBitWidth - 1)) - 1;
  switch (overflow) {
  case OverflowSemantics::ASSERT:
    return value < 0 || value > safeUpperBound ? std::nullopt : std::optional(value);
  case OverflowSemantics::SATURATE:
    return value < 0 ? DynamicAPInt(0) : (value < safeUpperBound ? value : safeUpperBound);
  case OverflowSemantics::WRAP:
  case OverflowSemantics::TRUNCATE:
    return positiveModulo(value, safeUpperBound + 1);
  }
  llvm_unreachable("unknown overflow semantics");
}
 
} // namespace llzk::cast