random big.Integer function

[einar-hjortdal]

Describe the feature

Generate random big.Integer in the range [0, n)
fn random_integer(n Integer) Integer
Similar to integer_from_bytes, integer_from_i64, integer_from_int, etc.

Use Case

Needed for Secure Remote Password and other crypto implementations.

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.7 79bedff

Environment details (OS name and version, etc.)

V full version: V 0.4.7 ace4e93.79bedff
OS: linux, Linux version 5.14.0-427.33.1.el9_4.x86_64 (mockbuild@pp-el9) (gcc (GCC) 11.4.1 20231218 (Red Hat 11.4.1-3), GNU ld version 2.35.2-43.el9) #1 SMP PREEMPT_DYNAMIC Thu Aug 29 12:00:49 CEST 2024
Processor: 8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz

getwd: /home/einar/Documents/projects/vlang/active/firebird
vexe: /home/einar/.local/lib64/v/v
vexe mtime: 2024-09-12 07:04:54

vroot: OK, value: /home/einar/.local/lib64/v
VMODULES: OK, value: /home/einar/.vmodules
VTMP: OK, value: /tmp/v_1001

Git version: git version 2.43.5
Git vroot status: weekly.2024.35-55-g79bedff1 (5 commit(s) behind V master)
.git/config present: true

CC version: cc (GCC) 11.4.1 20231218 (Red Hat 11.4.1-3)
thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9

Note

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[MarcusMWilliams]

👍

…

On Thu, Sep 12, 2024, 10:36 AM Einar Hjortdal ***@***.***> wrote: Describe the feature Generate random big.Integer in the range [0, n) fn random_integer(n Integer) Integer Similar to integer_from_bytes, integer_from_i64, integer_from_int, etc. Use Case Needed for Secure Remote Password and other crypto implementations. Proposed Solution *No response* Other Information *No response* Acknowledgements - I may be able to implement this feature request - This feature might incur a breaking change Version used V 0.4.7 79bedff Environment details (OS name and version, etc.) V full version: V 0.4.7 ace4e93.79bedff OS: linux, Linux version 5.14.0-427.33.1.el9_4.x86_64 ***@***.***) (gcc (GCC) 11.4.1 20231218 (Red Hat 11.4.1-3), GNU ld version 2.35.2-43.el9) #1 SMP PREEMPT_DYNAMIC Thu Aug 29 12:00:49 CEST 2024 Processor: 8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz getwd: /home/einar/Documents/projects/vlang/active/firebird vexe: /home/einar/.local/lib64/v/v vexe mtime: 2024-09-12 07:04:54 vroot: OK, value: /home/einar/.local/lib64/v VMODULES: OK, value: /home/einar/.vmodules VTMP: OK, value: /tmp/v_1001 Git version: git version 2.43.5 Git vroot status: weekly.2024.35-55-g79bedff1 (5 commit(s) behind V master) .git/config present: true CC version: cc (GCC) 11.4.1 20231218 (Red Hat 11.4.1-3) thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9 Note You can use the 👍 reaction to increase the issue's priority for developers. Please note that only the 👍 reaction to the issue itself counts as a vote. Other reactions and those to comments will not be taken into account. — Reply to this email directly, view it on GitHub <#22206>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ASHJW57X4LKRPBOJ2F6RJDTZWGYHFAVCNFSM6AAAAABODRLHRWVHI2DSMVQWIX3LMV43ASLTON2WKOZSGUZDENZTHA4TAOA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[einar-hjortdal]

@hungrybluedev you're the big.Integer man, right? 🙏

[einar-hjortdal]

Something like this maybe?

// new_random_big_integer creates a random `big.Integer` with range [0, n)
// panics if `n` is 0 or negative.
pub fn new_random_big_integer(n big.Integer) !big.Integer {
	if n.signum < 1 {
		return error('`n` cannot be 0 or negative.')
	}

	max := n - big.integer_from_int(1)
	len := max.bit_len()

	if len == 0 {
		// max must be 0
		return max
	}

	// k is the maximum byte length needed to encode a value < n
	k := (len + 7) / 8

	// b is the number of bits in the most significant byte of n-1
	get_b := fn [len] () u64 {
		b := u64(len % 8)
		if b == 0 {
			return 8
		}
		return b
	}
	b := get_b()

	mut result := big.Integer{}
	for found := false; found == false; {
		mut bytes := rand.read(k)!

		// Clear bits in the first byte to increase the probability that the result is < max
		bytes[0] &= u8(int(1 << b) - 1)

		result = big.integer_from_bytes(bytes)
		if result < max {
			found = true
		}
	}
	return result
}