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 (Field.ORDER).
You can create a new Field from everything "field-like" (bigint, integer number, decimal string, Field).
Example
Field(10n); // Field construction 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
Constructors
new Field(x)
new Field(x:
| string
| number
| bigint
| FieldConst
| FieldVar
| Field): Field
Coerce anything "field-like" (bigint, number, string, and Field) to a Field.
Parameters
• x:
| string
| number
| bigint
| FieldConst
| FieldVar
| Field
Returns
Source
Properties
value
value: FieldVar;
Source
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.
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sizeInBits
static sizeInBits: number = Fp.sizeInBits;
The size of a Field element in bits - 255.
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sizeInBytes
static sizeInBytes: number = BinableFp.sizeInBytes;
The size of a Field element in bytes - 32.
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Methods
add()
add(y: string | number | bigint | Field): Field
Add a field-like value to this Field element.
Parameters
• y: string | number | bigint | Field
Returns
A Field element equivalent to the modular addition of the two value.
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 (subtraction) to prove the sum is calculated correctly.
sum.sub(x).assertEquals(Field(-7));
sum.sub(Field(-7)).assertEquals(x);
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assertBool()
assertBool(message?: string): Bool
Prove that this Field is equal to 0 or 1. Returns the Field wrapped in a Bool.
If the assertion fails, the code throws an error.
Parameters
• message?: string
Returns
Source
assertEquals()
assertEquals(y: string | number | bigint | Field, message?: string): void
Assert that this Field is equal another "field-like" value.
Calling this function is equivalent to Field(...).equals(...).assertEquals(Bool(true)).
See Field.equals for more details.
Important: If an assertion fails, the code throws an error.
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
Source
assertGreaterThan()
assertGreaterThan(y: string | number | bigint | Field, message?: string): void
Assert that this Field is greater than another "field-like" value.
Note: This uses fewer constraints than x.greaterThan(y).assertTrue().
See Field.greaterThan for more details.
Important: If an assertion fails, the code throws an error.
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
Source
assertGreaterThanOrEqual()
assertGreaterThanOrEqual(y: string | number | bigint | Field, message?: string): void
Assert that this Field is greater than or equal to another "field-like" value.
Note: This uses fewer constraints than x.greaterThanOrEqual(y).assertTrue().
See Field.greaterThanOrEqual for more details.
Important: If an assertion fails, the code throws an error.
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
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assertLessThan()
assertLessThan(y: string | number | bigint | Field, message?: string): void
Assert that this Field is less than another "field-like" value.
Note: This uses fewer constraints than x.lessThan(y).assertTrue().
See Field.lessThan for more details.
Important: If an assertion fails, the code throws an error.
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
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assertLessThanOrEqual()
assertLessThanOrEqual(y: string | number | bigint | Field, message?: string): void
Assert that this Field is less than or equal to another "field-like" value.
Note: This uses fewer constraints than x.lessThanOrEqual(y).assertTrue().
See Field.lessThanOrEqual for more details.
Important: If an assertion fails, the code throws an error.
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
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assertNotEquals()
assertNotEquals(y: string | number | bigint | Field, message?: string): void
Assert that this Field does not equal another field-like value.
Note: This uses fewer constraints than x.equals(y).assertFalse().
Parameters
• y: string | number | bigint | Field
• message?: string
Returns
void
Example
x.assertNotEquals(0, "expect x to be non-zero");
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div()
div(y: string | number | bigint | Field): Field
Divide another "field-like" value through this Field.
Proves that the denominator is non-zero, or throws a "Division by zero" error.
Parameters
• y: string | number | bigint | Field
Returns
A Field element equivalent to the modular division of the two value.
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);
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equals()
equals(y: string | number | bigint | Field): 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.
Parameters
• y: string | number | bigint | Field
Returns
A Bool representing if this Field is equal another "field-like" value.
Example
Field(5).equals(5).assertEquals(Bool(true));
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greaterThan()
greaterThan(y: string | number | bigint | Field): 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.
Parameters
• y: string | number | bigint | Field
Returns
A Bool representing if this Field is greater than another "field-like" value.
Example
let isTrue = Field(5).greaterThan(3);
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
let isFalse = Field(1).div(2).greaterThan(Field(1).div(3); // in fact, 1/3 > 1/2
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greaterThanOrEqual()
greaterThanOrEqual(y: string | number | bigint | Field): 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.
Parameters
• y: string | number | bigint | Field
Returns
A Bool representing if this Field is greater than or equal another "field-like" value.
Example
let isTrue = Field(3).greaterThanOrEqual(3);
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
let isFalse = Field(1).div(2).greaterThanOrEqual(Field(1).div(3); // in fact, 1/3 > 1/2
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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.
Returns
A Field element that is equivalent to one divided by this element.
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.
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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.
Returns
this is Object
A boolean showing if this Field is a constant or not.
Example
console.log(Field(42).isConstant()); // true
Example
\@method myMethod(x: Field) {
console.log(x.isConstant()); // false
}
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isEven()
isEven(): Bool
Checks if this Field is even. Returns true for even elements and false for odd elements.
Returns
Example
let a = Field(5);
a.isEven(); // false
let b = Field(4);
b.isEven(); // true
Source
isOdd()
isOdd(): Bool
Checks if this Field is odd. Returns true for odd elements and false for even elements.
See Field.isEven for examples.
Returns
Source
lessThan()
lessThan(y: string | number | bigint | Field): 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.
Parameters
• y: string | number | bigint | Field
Returns
A Bool representing if this Field is less than another "field-like" value.
Example
let isTrue = Field(2).lessThan(3);
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
let isFalse = Field(1).div(3).lessThan(Field(1).div(2)); // in fact, 1/3 > 1/2
Source
lessThanOrEqual()
lessThanOrEqual(y: string | number | bigint | Field): 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.
Parameters
• y: string | number | bigint | Field
Returns
A Bool representing if this Field is less than or equal another "field-like" value.
Example
let isTrue = Field(3).lessThanOrEqual(3);
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
let isFalse = Field(1).div(3).lessThanOrEqual(Field(1).div(2)); // in fact, 1/3 > 1/2
Source
mul()
mul(y: string | number | bigint | Field): Field
Multiply another "field-like" value with this Field element.
Parameters
• y: string | number | bigint | Field
Returns
A Field element equivalent to the modular difference of the two value.
Example
const x = Field(3);
const product = x.mul(Field(5));
product.assertEquals(Field(15));
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neg()
neg(): Field
Negate a Field. This is equivalent to multiplying the Field by -1.
Returns
A Field element that is equivalent to the element multiplied 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.
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seal()
seal(): VarField | ConstantField
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.
Source
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.
Returns
A Field element equivalent to the square root of the Field element.
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.
Source
square()
square(): Field
Square this Field element.
Returns
A Field element equivalent to the multiplication of the Field element with itself.
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.
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sub()
sub(y: string | number | bigint | Field): Field
Subtract another "field-like" value from this Field element.
Parameters
• y: string | number | bigint | Field
Returns
A Field element equivalent to the modular difference of the two value.
Example
const x = Field(3);
const difference = x.sub(5);
difference.assertEquals(Field(-2));
Warning: This is a modular subtraction 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 subtraction (addition) to prove the difference is calculated correctly.
difference.add(Field(2)).assertEquals(x);
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toAuxiliary()
toAuxiliary(): []
This function is the implementation of Provable.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
[]
Source
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.
Returns
bigint
A bigint equivalent to the bigint representation of the Field.
Example
const someField = Field(42);
console.log(someField.toBigInt());
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toBits()
toBits(length: number): 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 254 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 254 bits. Prefer to pass a smaller length if possible.
Parameters
• length: number= 254
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.
Source
toConstant()
toConstant(): ConstantField
Create a Field element equivalent to this Field element's value, but is a constant. See Field.isConstant for more information about what is a constant Field.
Returns
A constant Field element equivalent to this Field element.
Example
const someField = Field(42);
someField.toConstant().assertEquals(someField); // Always true
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toFields()
toFields(): Field[]
This function is the implementation of Provable.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.
Source
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.
Returns
string
A string equivalent to the JSON representation of the Field.
Example
const someField = Field(42);
console.log(someField.toJSON());
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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.
Returns
string
A string equivalent to the string representation of the Field.
Example
const someField = Field(42);
console.log(someField.toString());
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check()
static check(): void
This function is the implementation of Provable.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
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empty()
static empty(): Field
Returns
Source
from()
static from(x: string | number | bigint | Field): Field
Parameters
• x: string | number | bigint | Field
Returns
Source
fromBits()
static fromBits(bits: (boolean | Bool)[]): 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. In this case, no more than 254 bits are allowed because some 255 bit integers do not fit into a single Field element.
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
• bits: (boolean | Bool)[]
Returns
A Field element matching the little endian binary representation of the given bytes array.
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fromBytes()
static fromBytes(bytes: number[]): 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 Field.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
• 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.
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fromFields()
static fromFields(fields: Field[]): Field
Implementation of Provable.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
• fields: Field[]
an array of length 1 serialized from Field elements.
Returns
The first Field element of the given array.
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fromJSON()
static fromJSON(json: string): 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
• json: string
Returns
A Field coerced from the given JSON string.
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fromValue()
static fromValue(x: string | number | bigint | Field): Field
Provable<Field>.fromValue()
Parameters
• x: string | number | bigint | Field
Returns
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random()
static random(): Field
A random Field element.
Returns
A random Field element.
Example
console.log(Field.random().toBigInt()); // Run this code twice!
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readBytes()
static readBytes<N>(bytes: number[], offset: NonNegativeInteger<N>): [Field, 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
• N extends number
Parameters
• bytes: number[]
• offset: NonNegativeInteger\<N>
Returns
[Field, number]
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sizeInFields()
static sizeInFields(): number
This function is the implementation of Provable.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.
Returns
number
A number representing the size of the Field type in terms of Field type itself.
Example
console.log(Field.sizeInFields()); // Prints 1
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toAuxiliary()
static toAuxiliary(): []
This function is the implementation of Provable.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
[]
Source
toBigint()
static toBigint(x: Field): bigint
Convert a Field element to a bigint.
Parameters
• x: Field
Returns
bigint
Source
toBytes()
static toBytes(x: Field): 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 Field.ORDER.
Parameters
• x: Field
Returns
number[]
An array of digits equal to the little-endian byte order of the given Field element.
Source
toFields()
static toFields(x: Field): Field[]
This function is the implementation of Provable.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
• x: Field
Returns
Field[]
A Field array of length 1 created from this Field.
Source
toInput()
static toInput(x: Field): {
fields: Field[];
}
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
• x: Field
Returns
{
fields: Field[];
}
An object where the fields key is a Field array of length 1 created from this Field.
fields
fields: Field[];
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toJSON()
static toJSON(x: Field): 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.
Parameters
• x: Field
Returns
string
A string equivalent to the JSON representation of the given Field.
Example
const someField = Field(42);
console.log(Field.toJSON(someField));
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toValue()
static toValue(x: Field): bigint
Provable<Field>.toValue()
Parameters
• x: Field
Returns
bigint