From aca3797f2371868e354abb68edc641e6210df9ce Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Wed, 18 Feb 2026 14:06:17 +0200
Subject: [PATCH] examples: improve pidigits.v using a much faster spigot
 algorithm from
 https://mail.python.org/pipermail/edu-sig/2012-December/010721.html

---
 examples/pidigits.v         | 66 +++++++++++--------------------------
 vlib/math/big/big.v         | 46 ++++++++++++++++++--------
 vlib/math/big/consts_test.v | 32 ++++++++++++++++++
 3 files changed, 84 insertions(+), 60 deletions(-)
 create mode 100644 vlib/math/big/consts_test.v

diff --git a/examples/pidigits.v b/examples/pidigits.v
index 85265cb87..27e462313 100644
--- a/examples/pidigits.v
+++ b/examples/pidigits.v
@@ -1,52 +1,26 @@
-module main
-
-import os
 import math.big
 
-const digits_to_print = os.args[1] or { '1000' }.int()
-
-const zero = big.integer_from_int(0)
-const one = big.integer_from_int(1)
-const two = big.integer_from_int(2)
-const three = big.integer_from_int(3)
-const four = big.integer_from_int(4)
-const ten = big.integer_from_int(10)
-
-fn main() {
-	unbuffer_stdout()
-	mut digits_printed := 0
-	mut k := one
-	mut n1 := four
-	mut n2 := three
-	mut d := one
-	mut u := zero
-	mut v := zero
-	mut w := zero
-	for {
-		u = n1 / d
-		v = n2 / d
-		u_int := u.int()
-		v_int := v.int()
-		if u_int == v_int {
-			print(u_int)
-			digits_printed++
-			if digits_printed >= digits_to_print {
-				println('')
-				return
+// pi_digits calculates the digits of Pi, based on https://mail.python.org/pipermail/edu-sig/2012-December/010721.html
+fn pi_digits(count int) {
+	mut n := count
+	mut k, mut a, mut b, mut a1, mut b1 := big.c2, big.c4, big.c1, big.c12, big.c4
+	mut p, mut q := k, k
+	for n > 0 {
+		p, q, k = k * k, (big.c2 * k) + big.c1, k + big.c1
+		a, b, a1, b1 = a1, b1, p * a + q * a1, p * b + q * b1
+		mut d := a / b
+		mut d1 := a1 / b1
+		for d == d1 {
+			print(d.int())
+			n--
+			a, a1 = big.c10 * (a % b), big.c10 * (a1 % b1)
+			d, d1 = a / b, a1 / b1
+			if n <= 0 {
+				break
 			}
-			to_minus := u * ten * d
-			n1 = n1 * ten - to_minus
-			n2 = n2 * ten - to_minus
-		} else {
-			k2 := k * two
-			u = n1 * (k2 - one)
-			v = n2 * two
-			w = n1 * (k - one)
-			n1 = u + v
-			u = n2 * (k + two)
-			n2 = w + u
-			d = d * (k2 + one)
-			k += one
 		}
 	}
 }
+
+pi_digits(arguments()[1] or { '100' }.int())
+println('')
diff --git a/vlib/math/big/big.v b/vlib/math/big/big.v
index 2c0cb7ab4..4a9357089 100644
--- a/vlib/math/big/big.v
+++ b/vlib/math/big/big.v
@@ -5,18 +5,36 @@ pub const zero_int = Integer{
 	signum:   0
 	is_const: true
 }
-pub const one_int = Integer{
-	digits:   [u64(1)]
-	signum:   1
-	is_const: true
-}
-pub const two_int = Integer{
-	digits:   [u64(2)]
-	signum:   1
-	is_const: true
-}
-pub const three_int = Integer{
-	digits:   [u64(3)]
-	signum:   1
-	is_const: true
+pub const one_int = positive_integer(1)
+pub const two_int = positive_integer(2)
+pub const three_int = positive_integer(3)
+
+pub const c0 = zero_int
+pub const c1 = positive_integer(1)
+pub const c2 = positive_integer(2)
+pub const c3 = positive_integer(3)
+pub const c4 = positive_integer(4)
+pub const c5 = positive_integer(5)
+pub const c6 = positive_integer(6)
+pub const c7 = positive_integer(7)
+pub const c8 = positive_integer(8)
+pub const c9 = positive_integer(9)
+pub const c10 = positive_integer(10)
+pub const c11 = positive_integer(11)
+pub const c12 = positive_integer(12)
+pub const c13 = positive_integer(13)
+pub const c14 = positive_integer(14)
+pub const c15 = positive_integer(15)
+pub const c16 = positive_integer(16)
+pub const c17 = positive_integer(17)
+pub const c18 = positive_integer(18)
+pub const c19 = positive_integer(19)
+pub const c20 = positive_integer(20)
+
+fn positive_integer(x int) Integer {
+	return Integer{
+		digits:   [u64(x)]
+		signum:   1
+		is_const: true
+	}
 }
diff --git a/vlib/math/big/consts_test.v b/vlib/math/big/consts_test.v
new file mode 100644
index 000000000..74edeb546
--- /dev/null
+++ b/vlib/math/big/consts_test.v
@@ -0,0 +1,32 @@
+import math.big
+
+fn test_named_consts() {
+	assert big.zero_int == big.integer_from_int(0)
+	assert big.one_int == big.integer_from_int(1)
+	assert big.two_int == big.integer_from_int(2)
+	assert big.three_int == big.integer_from_int(3)
+}
+
+fn test_indexed_consts() {
+	assert big.c0 == big.integer_from_int(0)
+	assert big.c1 == big.integer_from_int(1)
+	assert big.c2 == big.integer_from_int(2)
+	assert big.c3 == big.integer_from_int(3)
+	assert big.c4 == big.integer_from_int(4)
+	assert big.c5 == big.integer_from_int(5)
+	assert big.c6 == big.integer_from_int(6)
+	assert big.c7 == big.integer_from_int(7)
+	assert big.c8 == big.integer_from_int(8)
+	assert big.c9 == big.integer_from_int(9)
+	assert big.c10 == big.integer_from_int(10)
+	assert big.c11 == big.integer_from_int(11)
+	assert big.c12 == big.integer_from_int(12)
+	assert big.c13 == big.integer_from_int(13)
+	assert big.c14 == big.integer_from_int(14)
+	assert big.c15 == big.integer_from_int(15)
+	assert big.c16 == big.integer_from_int(16)
+	assert big.c17 == big.integer_from_int(17)
+	assert big.c18 == big.integer_from_int(18)
+	assert big.c19 == big.integer_from_int(19)
+	assert big.c20 == big.integer_from_int(20)
+}
-- 
2.39.5