Field
Class: Field
A Field is an element of a prime order finite field. Every other provable type is built using the Field type.
The field is the pasta base field of order 2^254 + 0x224698fc094cf91b992d30ed00000001 (ORDER).
You can create a new Field from everything "field-like" (bigint
, integer number
, decimal string
, Field
).
Example
Field(10n); // Field contruction from a big integer
Field(100); // Field construction from a number
Field("1"); // Field construction from a decimal string
Beware: Fields cannot be constructed from fractional numbers or alphanumeric strings:
Field(3.141); // ERROR: Cannot convert a float to a field element
Field("abc"); // ERROR: Invalid argument "abc"
Creating a Field from a negative number can result in unexpected behavior if you are not familiar with modular arithmetic.
Example
const x = Field(-1); // Valid Field construction from negative number
const y = Field(Field.ORDER - 1n); // equivalent to `x`
Important: All the functions defined on a Field (arithmetic, logic, etc.) take their arguments as "field-like". A Field itself is also defined as a "field-like" element.
Param
the value to convert to a Field
Table of contents
Constructors
Properties
Methods
- #compare
- #toConstant
- add
- assertBool
- assertEquals
- assertGreaterThan
- assertGreaterThanOrEqual
- assertLessThan
- assertLessThanOrEqual
- assertNotEquals
- div
- equals
- greaterThan
- greaterThanOrEqual
- inv
- isConstant
- isEven
- isZero
- lessThan
- lessThanOrEqual
- mul
- neg
- rangeCheckHelper
- seal
- sqrt
- square
- sub
- toAuxiliary
- toBigInt
- toBits
- toConstant
- toFields
- toJSON
- toString
- #checkBitLength
- #isField
- #toConst
- #toVar
- check
- from
- fromBits
- fromBytes
- fromFields
- fromJSON
- random
- readBytes
- sizeInBytes
- sizeInFields
- toAuxiliary
- toBytes
- toFields
- toInput
- toJSON
Constructors
constructor
• new Field(x
)
Coerce anything "field-like" (bigint, number, string, and Field) to a Field.
Parameters
Name | Type |
---|---|
x | string | number | bigint | Uint8Array | FieldVar | Field |
Defined in
Properties
value
• value: FieldVar
Defined in
ORDER
▪ Static
ORDER: bigint
= Fp.modulus
The order of the pasta curve that Field type build on as a bigint
.
Order of the Field is 28948022309329048855892746252171976963363056481941560715954676764349967630337.
Defined in
Methods
#compare
▸ Private
#compare(y
): Object
Parameters
Name | Type |
---|---|
y | FieldVar |
Returns
Object
Name | Type |
---|---|
less | Bool |
lessOrEqual | Bool |
Defined in
#toConstant
▸ Private
#toConstant(name
): ConstantField
Parameters
Name | Type |
---|---|
name | string |
Returns
Defined in
add
▸ add(y
): Field
Add a "field-like" value to this Field element.
Example
const x = Field(3);
const sum = x.add(5);
sum.assertEquals(Field(8));
Warning: This is a modular addition in the pasta field.
Example
const x = Field(1);
const sum = x.add(Field(-7));
// If you try to print sum - `console.log(sum.toBigInt())` - you will realize that it prints a very big integer because this is modular arithmetic, and 1 + (-7) circles around the field to become p - 6.
// You can use the reverse operation of addition (substraction) to prove the sum is calculated correctly.
sum.sub(x).assertEquals(Field(-7));
sum.sub(Field(-7)).assertEquals(x);
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Field element equivalent to the modular addition of the two value.
Defined in
assertBool
▸ assertBool(message?
): void
Assert that this Field is equal to 1 or 0 as a "field-like" value.
Calling this function is equivalent to Bool.or(Field(...).equals(1), Field(...).equals(0)).assertEquals(Bool(true))
.
Important: If an assertion fails, the code throws an error.
Parameters
Name | Type |
---|---|
message? | string |
Returns
void
Defined in
assertEquals
▸ assertEquals(y
, message?
): void
Assert that this Field is equal another "field-like" value.
Calling this function is equivalent to Field(...).equals(...).assertEquals(Bool(true))
.
See equals for more details.
Important: If an assertion fails, the code throws an error.
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
assertGreaterThan
▸ assertGreaterThan(y
, message?
): void
Assert that this Field is greater than another "field-like" value.
Calling this function is equivalent to Field(...).greaterThan(...).assertEquals(Bool(true))
.
See greaterThan for more details.
Important: If an assertion fails, the code throws an error.
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
assertGreaterThanOrEqual
▸ assertGreaterThanOrEqual(y
, message?
): void
Assert that this Field is greater than or equal to another "field-like" value.
Calling this function is equivalent to Field(...).greaterThanOrEqual(...).assertEquals(Bool(true))
.
See greaterThanOrEqual for more details.
Important: If an assertion fails, the code throws an error.
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
assertLessThan
▸ assertLessThan(y
, message?
): void
Assert that this Field is less than another "field-like" value.
Calling this function is equivalent to Field(...).lessThan(...).assertEquals(Bool(true))
.
See lessThan for more details.
Important: If an assertion fails, the code throws an error.
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
assertLessThanOrEqual
▸ assertLessThanOrEqual(y
, message?
): void
Assert that this Field is less than or equal to another "field-like" value.
Calling this function is equivalent to Field(...).lessThanOrEqual(...).assertEquals(Bool(true))
.
See lessThanOrEqual for more details.
Important: If an assertion fails, the code throws an error.
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
assertNotEquals
▸ assertNotEquals(y
, message?
): void
Assert that this Field does not equal another field-like value.
Note: This uses fewer constraints than x.equals(y).assertFalse()
.
Example
x.assertNotEquals(0, "expect x to be non-zero");
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
message? | string |
Returns
void
Defined in
div
▸ div(y
): Field
Divide another "field-like" value through this Field.
Proves that the denominator is non-zero, or throws a "Division by zero" error.
Example
const x = Field(6);
const quotient = x.div(Field(3));
quotient.assertEquals(Field(2));
Warning: This is a modular division in the pasta field. You can think this as the reverse operation of modular multiplication.
Example
const x = Field(2);
const y = Field(5);
const quotient = x.div(y);
// If you try to print quotient - `console.log(quotient.toBigInt())` - you will realize that it prints a very big integer because this is a modular inverse.
// You can use the reverse operation of division (multiplication) to prove the quotient is calculated correctly.
quotient.mul(y).assertEquals(x);
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Field element equivalent to the modular division of the two value.
Defined in
equals
▸ equals(y
): Bool
Check if this Field is equal another "field-like" value. Returns a Bool, which is a provable type and can be used to prove the validity of this statement.
Example
Field(5).equals(5).assertEquals(Bool(true));
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Bool representing if this Field is equal another "field-like" value.
Defined in
greaterThan
▸ greaterThan(y
): Bool
Check if this Field is greater than another "field-like" value. Returns a Bool, which is a provable type and can be used to prove the validity of this statement.
Example
Field(5).greaterThan(3).assertEquals(Bool(true));
Warning: Comparison methods currently only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Warning: As this method compares the bigint value of a Field, it can result in unexpected behaviour when used with negative inputs or modular division.
Example
Field(1).div(Field(2)).greaterThan(Field(1).div(Field(3))).assertEquals(Bool(true)); // This code will throw an error
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Bool representing if this Field is greater than another "field-like" value.
Defined in
greaterThanOrEqual
▸ greaterThanOrEqual(y
): Bool
Check if this Field is greater than or equal another "field-like" value. Returns a Bool, which is a provable type and can be used to prove the validity of this statement.
Example
Field(3).greaterThanOrEqual(3).assertEquals(Bool(true));
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Warning: As this method compares the bigint value of a Field, it can result in unexpected behaviour when used with negative inputs or modular division.
Example
Field(1).div(Field(2)).greaterThanOrEqual(Field(1).div(Field(3))).assertEquals(Bool(true)); // This code will throw an error
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Bool representing if this Field is greater than or equal another "field-like" value.
Defined in
inv
▸ inv(): Field
Modular inverse of this Field element. Equivalent to 1 divided by this Field, in the sense of modular arithmetic.
Proves that this Field is non-zero, or throws a "Division by zero" error.
Example
const someField = Field(42);
const inverse = someField.inv();
inverse.assertEquals(Field(1).div(example)); // This statement is always true regardless of the value of `someField`
Warning: This is a modular inverse. See div method for more details.
Returns
A Field element that is equivalent to one divided by this element.
Defined in
isConstant
▸ isConstant(): this is Object
Check whether this Field element is a hard-coded constant in the constraint system. If a Field is constructed outside a zkApp method, it is a constant.
Example
console.log(Field(42).isConstant()); // true
Example
\@method myMethod(x: Field) {
console.log(x.isConstant()); // false
}
Returns
this is Object
A boolean
showing if this Field is a constant or not.
Defined in
isEven
▸ isEven(): Bool
Checks if this Field is even. Returns true
for even elements and false
for odd elements.
Example
let a = Field(5);
a.isEven(); // false
a.isEven().assertTrue(); // throws, as expected!
let b = Field(4);
b.isEven(); // true
b.isEven().assertTrue(); // does not throw, as expected!
Returns
Defined in
isZero
▸ isZero(): Bool
Deprecated
use x.equals(0)
which is equivalent
Returns
Defined in
lessThan
▸ lessThan(y
): Bool
Check if this Field is less than another "field-like" value. Returns a Bool, which is a provable type and can be used prove to the validity of this statement.
Example
Field(2).lessThan(3).assertEquals(Bool(true));
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Warning: As this method compares the bigint value of a Field, it can result in unexpected behavior when used with negative inputs or modular division.
Example
Field(1).div(Field(3)).lessThan(Field(1).div(Field(2))).assertEquals(Bool(true)); // This code will throw an error
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Bool representing if this Field is less than another "field-like" value.
Defined in
lessThanOrEqual
▸ lessThanOrEqual(y
): Bool
Check if this Field is less than or equal to another "field-like" value. Returns a Bool, which is a provable type and can be used to prove the validity of this statement.
Example
Field(3).lessThanOrEqual(3).assertEquals(Bool(true));
Warning: Comparison methods only support Field elements of size <= 253 bits in provable code. The method will throw if one of the inputs exceeds 253 bits.
Warning: As this method compares the bigint value of a Field, it can result in unexpected behaviour when used with negative inputs or modular division.
Example
Field(1).div(Field(3)).lessThanOrEqual(Field(1).div(Field(2))).assertEquals(Bool(true)); // This code will throw an error
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Bool representing if this Field is less than or equal another "field-like" value.
Defined in
mul
▸ mul(y
): Field
Multiply another "field-like" value with this Field element.
Example
const x = Field(3);
const product = x.mul(Field(5));
product.assertEquals(Field(15));
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Field element equivalent to the modular difference of the two value.
Defined in
neg
▸ neg(): Field
Negate a Field. This is equivalent to multiplying the Field by -1.
Example
const negOne = Field(1).neg();
negOne.assertEquals(-1);
Example
const someField = Field(42);
someField.neg().assertEquals(someField.mul(Field(-1))); // This statement is always true regardless of the value of `someField`
Warning: This is a modular negation. For details, see the sub method.
Returns
A Field element that is equivalent to the element multiplied by -1.
Defined in
rangeCheckHelper
▸ rangeCheckHelper(length
): Field
Create a new Field element from the first length
bits of this Field element.
The length
has to be a multiple of 16, and has to be between 0 and 255, otherwise the method throws.
As Field elements are represented using little endian binary representation,
the resulting Field element will equal the original one if it fits in length
bits.
Parameters
Name | Type | Description |
---|---|---|
length | number | The number of bits to take from this Field element. |
Returns
A Field element that is equal to the length
of this Field element.
Defined in
seal
▸ seal(): Field
Warning: This function is mainly for internal use. Normally it is not intended to be used by a zkApp developer.
In o1js, addition and scaling (multiplication of variables by a constant) of variables is represented as an AST - abstract syntax tree. For example, the expression x.add(y).mul(2)
is represented as Scale(2, Add(x, y))
.
A new internal variable is created only when the variable is needed in a multiplicative or any higher level constraint (for example multiplication of two Field elements) to represent the operation.
The seal()
function tells o1js to stop building an AST and create a new variable right away.
Returns
A Field element that is equal to the result of AST that was previously on this Field element.
Defined in
sqrt
▸ sqrt(): Field
Take the square root of this Field element.
Proves that the Field element has a square root in the finite field, or throws if it doesn't.
Example
let z = x.sqrt();
z.mul(z).assertEquals(x); // true for every `x`
Warning: This is a modular square root, which is any number z that satisfies z*z = x (mod p). Note that, if a square root z exists, there also exists a second one, -z (which is different if z != 0). Therefore, this method leaves an adversarial prover the choice between two different values to return.
Returns
A Field element equivalent to the square root of the Field element.
Defined in
square
▸ square(): Field
Square this Field element.
Example
const someField = Field(7);
const square = someField.square();
square.assertEquals(someField.mul(someField)); // This statement is always true regardless of the value of `someField`
** Warning: This is a modular multiplication. See mul()
method for more details.
Returns
A Field element equivalent to the multiplication of the Field element with itself.
Defined in
sub
▸ sub(y
): Field
Substract another "field-like" value from this Field element.
Example
const x = Field(3);
const difference = x.sub(5);
difference.assertEquals(Field(-2));
Warning: This is a modular substraction in the pasta field.
Example
const x = Field(1);
const difference = x.sub(Field(2));
// If you try to print difference - `console.log(difference.toBigInt())` - you will realize that it prints a very big integer because this is modular arithmetic, and 1 - 2 circles around the field to become p - 1.
// You can use the reverse operation of substraction (addition) to prove the difference is calculated correctly.
difference.add(Field(2)).assertEquals(x);
Parameters
Name | Type |
---|---|
y | string | number | bigint | Field |
Returns
A Field element equivalent to the modular difference of the two value.
Defined in
toAuxiliary
▸ toAuxiliary(): []
This function is the implementation of toAuxiliary for the Field type.
As the primitive Field type has no auxiliary data associated with it, this function will always return an empty array.
Returns
[]
Defined in
toBigInt
▸ toBigInt(): bigint
Serialize the Field to a bigint, e.g. for printing. Trying to print a Field without this function will directly stringify the Field object, resulting in unreadable output.
Warning: This operation does not affect the circuit and can't be used to prove anything about the bigint representation of the Field. Use the operation only during debugging.
Example
const someField = Field(42);
console.log(someField.toBigInt());
Returns
bigint
A bigint equivalent to the bigint representation of the Field.
Defined in
toBits
▸ toBits(length?
): Bool
[]
Returns an array of Bool elements representing little endian binary representation of this Field element.
If you use the optional length
argument, proves that the field element fits in length
bits.
The length
has to be between 0 and 255 and the method throws if it isn't.
Warning: The cost of this operation in a zk proof depends on the length
you specify,
which by default is 255 bits. Prefer to pass a smaller length
if possible.
Parameters
Name | Type | Description |
---|---|---|
length? | number | the number of bits to fit the element. If the element does not fit in length bits, the functions throws an error. |
Returns
Bool
[]
An array of Bool element representing little endian binary representation of this Field.
Defined in
toConstant
▸ toConstant(): ConstantField
Create a Field element equivalent to this Field element's value, but is a constant. See isConstant for more information about what is a constant Field.
Example
const someField = Field(42);
someField.toConstant().assertEquals(someField); // Always true
Returns
A constant Field element equivalent to this Field element.
Defined in
toFields
▸ toFields(): Field
[]
This function is the implementation of toFields for the Field type.
The result will be always an array of length 1, where the first and only element equals the Field itself.
Returns
Field
[]
A Field array of length 1 created from this Field.
Defined in
toJSON
▸ toJSON(): string
Serialize the Field to a JSON string, e.g. for printing. Trying to print a Field without this function will directly stringify the Field object, resulting in unreadable output.
Warning: This operation does not affect the circuit and can't be used to prove anything about the JSON string representation of the Field. Use the operation only during debugging.
Example
const someField = Field(42);
console.log(someField.toJSON());
Returns
string
A string equivalent to the JSON representation of the Field.
Defined in
toString
▸ toString(): string
Serialize the Field to a string, e.g. for printing. Trying to print a Field without this function will directly stringify the Field object, resulting in unreadable output.
Warning: This operation does not affect the circuit and can't be used to prove anything about the string representation of the Field. Use the operation only during debugging.
Example
const someField = Field(42);
console.log(someField.toString());
Returns
string
A string equivalent to the string representation of the Field.
Defined in
#checkBitLength
▸ Static
Private
#checkBitLength(name
, length
): void
Parameters
Name | Type |
---|---|
name | string |
length | number |
Returns
void
Defined in
#isField
▸ Static
Private
#isField(x
): x is Field
Parameters
Name | Type |
---|---|
x | string | number | bigint | Uint8Array | FieldVar | Field |
Returns
x is Field
Defined in
#toConst
▸ Static
Private
#toConst(x
): Uint8Array
Parameters
Name | Type |
---|---|
x | string | number | bigint | ConstantField |
Returns
Uint8Array
Defined in
#toVar
▸ Static
Private
#toVar(x
): FieldVar
Parameters
Name | Type |
---|---|
x | string | number | bigint | Field |
Returns
Defined in
check
▸ Static
check(): void
This function is the implementation of check in Field type.
As any field element can be a Field, this function does not create any assertions, so it does nothing.
Returns
void
Defined in
from
▸ Static
from(x
): Field
Parameters
Name | Type |
---|---|
x | string | number | bigint | Field |
Returns
Defined in
fromBits
▸ Static
fromBits(bits
): Field
Convert a bit array into a Field element using little endian binary representation
The method throws if the given bits do not fit in a single Field element. A Field element can be at most 255 bits.
Important: If the given bytes
array is an array of booleans
or Bool elements that all are constant
, the resulting Field element will be a constant as well. Or else, if the given array is a mixture of constants and variables of Bool type, the resulting Field will be a variable as well.
Parameters
Name | Type |
---|---|
bits | (boolean | Bool )[] |
Returns
A Field element matching the little endian binary representation of the given bytes
array.
Defined in
fromBytes
▸ Static
fromBytes(bytes
): Field
Coerce a new Field element using the little-endian representation of the given bytes
array.
Note that the given bytes
array may have at most 32 elements as the Field is a finite-field
in the order of ORDER.
Warning: This operation does not affect the circuit and can't be used to prove anything about the byte representation of the Field.
Parameters
Name | Type | Description |
---|---|---|
bytes | number [] | The bytes array to coerce the Field from. |
Returns
A new Field element created using the little-endian representation of the given bytes
array.
Defined in
fromFields
▸ Static
fromFields(fields
): Field
Implementation of fromFields for the Field type.
Warning: This function is designed for internal use. It is not intended to be used by a zkApp developer.
Creates a Field from an array of Fields of length 1.
Parameters
Name | Type | Description |
---|---|---|
fields | Field [] | an array of length 1 serialized from Field elements. |
Returns
The first Field element of the given array.
Defined in
fromJSON
▸ Static
fromJSON(json
): Field
Deserialize a JSON string containing a "field-like" value into a Field element.
Warning: This operation does not affect the circuit and can't be used to prove anything about the string representation of the Field.
Parameters
Name | Type |
---|---|
json | string |
Returns
A Field coerced from the given JSON string.
Defined in
random
▸ Static
random(): Field
A random Field element.
Example
console.log(Field.random().toBigInt()); // Run this code twice!
Returns
A random Field element.
Defined in
readBytes
▸ Static
readBytes<N
>(bytes
, offset
): [value: Field, offset: number]
Part of the Binable
interface.
Warning: This function is for internal use. It is not intended to be used by a zkApp developer.
Type parameters
Name | Type |
---|---|
N | extends number |
Parameters
Name | Type |
---|---|
bytes | number [] |
offset | NonNegativeInteger <N > |
Returns
[value: Field, offset: number]
Defined in
sizeInBytes
▸ Static
sizeInBytes(): number
Warning: This function is mainly for internal use. Normally it is not intended to be used by a zkApp developer.
As all Field elements have 31 bits, this function returns 31.
Returns
number
The size of a Field element - 31.
Defined in
sizeInFields
▸ Static
sizeInFields(): number
This function is the implementation of sizeInFields for the Field type.
Size of the Field type is 1, as it is the primitive type. This function returns a regular number, so you cannot use it to prove something on chain. You can use it during debugging or to understand the memory complexity of some type.
Example
console.log(Field.sizeInFields()); // Prints 1
Returns
number
A number representing the size of the Field type in terms of Field type itself.
Defined in
toAuxiliary
▸ Static
toAuxiliary(): []
This function is the implementation of toAuxiliary for the Field type.
As the primitive Field type has no auxiliary data associated with it, this function will always return an empty array.
Returns
[]
Defined in
toBytes
▸ Static
toBytes(x
): number
[]
Create an array of digits equal to the little-endian byte order of the given Field element.
Note that the array has always 32 elements as the Field is a finite-field
in the order of ORDER.
Parameters
Name | Type |
---|---|
x | Field |
Returns
number
[]
An array of digits equal to the little-endian byte order of the given Field element.
Defined in
toFields
▸ Static
toFields(x
): Field
[]
This function is the implementation of toFields for the Field type.
Static function to serializes a Field into an array of Field elements. This will be always an array of length 1, where the first and only element equals the given parameter itself.
Parameters
Name | Type |
---|---|
x | Field |
Returns
Field
[]
A Field array of length 1 created from this Field.
Defined in
toInput
▸ Static
toInput(x
): Object
Warning: This function is mainly for internal use. Normally it is not intended to be used by a zkApp developer.
This function is the implementation of ProvableExtended.toInput()
for the Field type.
Parameters
Name | Type |
---|---|
x | Field |
Returns
Object
An object where the fields
key is a Field array of length 1 created from this Field.
Name | Type |
---|---|
fields | Field [] |
Defined in
toJSON
▸ Static
toJSON(x
): string
Serialize the given Field element to a JSON string, e.g. for printing. Trying to print a Field without this function will directly stringify the Field object, resulting in unreadable output.
Warning: This operation does not affect the circuit and can't be used to prove anything about the JSON string representation of the Field. Use the operation only during debugging.
Example
const someField = Field(42);
console.log(Field.toJSON(someField));
Parameters
Name | Type |
---|---|
x | Field |
Returns
string
A string equivalent to the JSON representation of the given Field.