Safe Arithmetic

Same operations as core arithmetic, but returning two handles: (ebool success, result). When success is false, the result is always 0.

Use safe arithmetic when your contract needs to detect and handle overflow or underflow without leaking information through transaction reverts.

Supported types: euint16, euint256, eint16, eint256

Usage

(ebool ok, euint256 newBalance) = Nox.safeAdd(balance, amount);
// Use select to keep the old balance on failure
euint256 finalBalance = Nox.select(ok, newBalance, balance);
Nox.allowThis(finalBalance);

safeAdd

function safeAdd(euint256 a, euint256 b) internal returns (ebool success, euint256 result)

Addition with overflow detection. Returns success = false and result = 0 on overflow.

• Unsigned: success = false when a + b > MAX
• Signed: success = false when the result exceeds MAX or goes below MIN

Example (Uint8)	success	result	Reason
SafeAdd(200, 100)	false	0	Overflow
SafeAdd(255, 1)	false	0	Overflow
SafeAdd(200, 55)	true	255	No overflow
SafeAdd(100, 50)	true	150	No overflow
SafeAdd(0, 0)	true	0	No overflow

Example (Int8)	success	result	Reason
SafeAdd(127, 1)	false	0	Positive overflow
SafeAdd(-128, -1)	false	0	Negative overflow
SafeAdd(100, 20)	true	120	No overflow
SafeAdd(-50, -50)	true	-100	No overflow

safeSub

function safeSub(euint256 a, euint256 b) internal returns (ebool success, euint256 result)

Subtraction with underflow detection. Returns success = false and result = 0 on underflow.

• Unsigned: success = false when a - b < 0
• Signed: success = false when the result exceeds MAX or goes below MIN

Example (Uint8)	success	result	Reason
SafeSub(0, 1)	false	0	Underflow
SafeSub(50, 100)	false	0	Underflow
SafeSub(100, 50)	true	50	No underflow
SafeSub(0, 0)	true	0	No underflow

Example (Int8)	success	result	Reason
SafeSub(-128, 1)	false	0	Signed underflow
SafeSub(127, -1)	false	0	Equivalent to 127 + 1, overflow
SafeSub(0, 0)	true	0	No underflow

safeMul

function safeMul(euint256 a, euint256 b) internal returns (ebool success, euint256 result)

Multiplication with overflow detection. Returns success = false and result = 0 on overflow.

• Unsigned: success = false when a * b > MAX
• Signed: success = false when the result exceeds MAX or goes below MIN

Example (Uint8)	success	result	Reason
SafeMul(16, 16)	false	0	Overflow
SafeMul(15, 17)	false	0	Overflow
SafeMul(15, 16)	true	240	No overflow
SafeMul(0, x)	true	0	Zero is absorbing
SafeMul(1, x)	true	x	Identity, no overflow

Example (Int8)	success	result	Reason
SafeMul(-128, -1)	false	0	Overflow (128 > MAX)
SafeMul(127, 2)	false	0	Overflow
SafeMul(64, 2)	false	0	Overflow (128 > MAX)
SafeMul(-1, -1)	true	1	No overflow
SafeMul(63, 2)	true	126	No overflow

safeDiv

function safeDiv(euint256 a, euint256 b) internal returns (ebool success, euint256 result)

Division with error detection. Returns success = false and result = 0 on division by zero or signed overflow (MIN / -1).

• Unsigned: success = false when dividing by zero
• Signed: success = false when dividing by zero or MIN / -1

Example (Uint8)	success	result	Reason
SafeDiv(255, 0)	false	0	Division by zero
SafeDiv(0, 0)	false	0	Division by zero
SafeDiv(100, 3)	true	33	Normal division
SafeDiv(1, 2)	true	0	Truncated toward zero
SafeDiv(0, 5)	true	0	Zero numerator

Example (Int8)	success	result	Reason
SafeDiv(100, 0)	false	0	Division by zero
SafeDiv(0, 0)	false	0	Division by zero
SafeDiv(-128, -1)	false	0	Signed overflow (MIN / -1)
SafeDiv(-7, 2)	true	-3	Truncated toward zero (not floor)
SafeDiv(50, 5)	true	10	Normal division