Field Operations

Field operations

Miden assembly provides a set of instructions which can perform operations with raw field elements. These instructions are described in the tables below.

While most operations place no restrictions on inputs, some operations expect inputs to be binary values, and fail if executed with non-binary inputs.

For instructions where one or more operands can be provided as immediate parameters (e.g., add and add.b), we provide stack transition diagrams only for the non-immediate version. For the immediate version, it can be assumed that the operand with the specified name is not present on the stack.

Assertions and tests

Instruction	Stack_input	Stack_output	Notes
assert - (1 cycle)	[a, ...]	[...]	If $a = 1$, removes it from the stack. Fails if $a \ne 1$
assertz - (2 cycles)	[a, ...]	[...]	If $a = 0$, removes it from the stack, Fails if $a \ne 0$
assert_eq - (2 cycles)	[b, a, ...]	[...]	If $a = b$, removes them from the stack. Fails if $a \ne b$
assert_eqw - (11 cycles)	[B, A, ...]	[...]	If $A = B$, removes them from the stack. Fails if $A \ne B$

The above instructions can also be parametrized with an error message which can be specified either directly or via a named constant. For example:

u32assert.err="Division by zero"
u32assert.err=MY_CONSTANT

The message is hashed and turned into a field element. If the error code is omitted, the default value of $0$ is assumed.

Arithmetic and Boolean operations

The arithmetic operations below are performed in a 64-bit prime field defined by modulus $p = 2^{64} - 2^{32} + 1$. This means that overflow happens after a value exceeds $p$.

Warning: div performs field division, not integer floor division. Field division computes $a \cdot b^{-1} \bmod p$, which bears no relation to $\lfloor a / b \rfloor$ and will produce unexpected results for most integer use cases. For integer floor division, use u32div instead.

Instruction	Stack_input	Stack_output	Notes
add - (1 cycle) add.b - (1-2 cycle)	[b, a, ...]	[c, ...]	$c \leftarrow (a + b) \mod p$
sub - (2 cycles) sub.b - (2 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow (a - b) \mod p$
mul - (1 cycle) mul.b - (2 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow (a \cdot b) \mod p$
div - (2 cycles) div.b - (2 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow (a \cdot b^{-1}) \mod p$ Fails if $b = 0$ Note: this is field division, not integer floor division. Use u32div for floor division.
neg - (1 cycle)	[a, ...]	[b, ...]	$b \leftarrow -a \mod p$
inv - (1 cycle)	[a, ...]	[b, ...]	$b \leftarrow a^{-1} \mod p$ Fails if $a = 0$
pow2 - (16 cycles)	[a, ...]	[b, ...]	$b \leftarrow 2^a$ Fails if $a > 63$
exp.uxx - (9 + xx cycles) exp.b - (9 + log2(b) cycles)	[b, a, ...]	[c, ...]	$c \leftarrow a^b$ Fails if xx is outside [0, 63) exp is equivalent to exp.u64 and needs 73 cycles
ilog2 - (66 cycles)	[a, ...]	[b, ...]	$b \leftarrow \lfloor{log_2{a}}\rfloor$ Fails if $a = 0$
not - (1 cycle)	[a, ...]	[b, ...]	$b \leftarrow 1 - a$ Fails if $a > 1$
and - (1 cycle)	[b, a, ...]	[c, ...]	$c \leftarrow a \cdot b$ Fails if $max(a, b) > 1$
or - (1 cycle)	[b, a, ...]	[c, ...]	$c \leftarrow a + b - a \cdot b$ Fails if $max(a, b) > 1$
xor - (7 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow a + b - 2 \cdot a \cdot b$ Fails if $max(a, b) > 1$

Comparison operations

Instruction	Stack_input	Stack_output	Notes
eq - (1 cycle) eq.b - (1-2 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a=b 0, & \text{otherwise}\ \end{cases}$
neq - (2 cycle) neq.b - (2-3 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a \ne b 0, & \text{otherwise}\ \end{cases}$
lt - (17 cycles) lt.b - (18 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a < b 0, & \text{otherwise}\ \end{cases}$
lte - (18 cycles) lte.b - (19 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a \le b 0, & \text{otherwise}\ \end{cases}$
gt - (16 cycles) gt.b - (17 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a > b 0, & \text{otherwise}\ \end{cases}$
gte - (17 cycles) gte.b - (18 cycles)	[b, a, ...]	[c, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a \ge b 0, & \text{otherwise}\ \end{cases}$
is_odd - (6 cycles)	[a, ...]	[b, ...]	$b \leftarrow \begin{cases} 1, & \text{if}\ a \text{ is odd} 0, & \text{otherwise}\ \end{cases}$
eqw - (15 cycles)	[A, B, ...]	[c, A, B, ...]	$c \leftarrow \begin{cases} 1, & \text{if}\ a_i = b_i \; \forall i \in \{0, 1, 2, 3\} 0, & \text{otherwise}\ \end{cases}$

Extension Field Operations

All operations in this section are defined over the quadratic extension field $\mathbb{F}_p[x] / (x^2 - 7)$, with modulus $p = 2^{64} - 2^{32} + 1$.

Instruction	Stack_input	Stack_output	Notes
ext2add - (5 cycles)	[b0, b1, a0, a1, ...]	[c0, c1, ...]	$c0 \leftarrow (a0 + b0) \mod p$ and $c1 \leftarrow (a1 + b1) \mod p$
ext2sub - (7 cycles)	[b0, b1, a0, a1, ...]	[c0, c1, ...]	$c0 \leftarrow (a0 - b0) \mod p$ and $c1 \leftarrow (a1 - b1) \mod p$
ext2mul - (3 cycles)	[b0, b1, a0, a1, ...]	[c0, c1, ...]	$c0 \leftarrow a0b0 - 7a1b1 \mod p$ and $c1 \leftarrow a0b0 + a1b0 \mod p$
ext2neg - (4 cycles)	[a0, a1, ...]	[a0', a1', ...]	$a0' \leftarrow -a0$ and $a1' \leftarrow -a1$
ext2inv - (8 cycles)	[a0, a1, ...]	[a0', a1', ...]	$a' \leftarrow a^{-1}$ in $\mathbb{F}_p[x]/(x^2 - 7)$ Fails if $a = 0$
ext2div - (11 cycles)	[b0, b1, a0, a1, ...]	[c0, c1,]	$c \leftarrow a \cdot b^{-1}$ in $\mathbb{F}_p[x]/(x^2 - 7)$ Fails if $b=0$