--- /n/sources/plan9/sys/include/mp.h	Wed Jun 26 23:50:48 2024
+++ /sys/include/mp.h	Wed Jun 26 23:59:55 2024
@@ -38,6 +38,8 @@
 
 /* random bits */
 mpint*	mprand(int bits, void (*gen)(uchar*, int), mpint *b);
+/* return uniform random [0..n-1] */
+mpint*	mpnrand(mpint *n, void (*gen)(uchar*, int), mpint *b);
 
 /* conversion */
 mpint*	strtomp(char*, char**, int, mpint*);	/* ascii */
--- /n/sources/plan9/sys/include/ape/mp.h	Wed Jun 26 23:50:56 2024
+++ /sys/include/ape/mp.h	Thu Jun 27 00:03:04 2024
@@ -47,6 +47,8 @@
 
 /* random bits */
 mpint*	mprand(int bits, void (*gen)(uchar*, int), mpint *b);
+/* return uniform random [0..n-1] */
+mpint*	mpnrand(mpint *n, void (*gen)(uchar*, int), mpint *b);
 
 /* conversion */
 mpint*	strtomp(char*, char**, int, mpint*);	/* ascii */
--- /n/sources/plan9/sys/man/2/mp	Wed Jun 26 23:51:06 2024
+++ /sys/man/2/mp	Wed Jun 26 23:59:55 2024
@@ -1,6 +1,6 @@
 .TH MP 2
 .SH NAME
-mpsetminbits, mpnew, mpfree, mpbits, mpnorm, mpcopy, mpassign, mprand, strtomp, mpfmt,mptoa, betomp, mptobe, mptober, letomp, mptole, mptolel, mptoui, uitomp, mptoi, itomp, uvtomp, mptouv, vtomp, mptov, mpdigdiv, mpadd, mpsub, mpleft, mpright, mpmul, mpexp, mpmod, mpdiv, mpcmp, mpextendedgcd, mpinvert, mpsignif, mplowbits0, mpvecdigmuladd, mpvecdigmulsub, mpvecadd, mpvecsub, mpveccmp, mpvecmul, mpmagcmp, mpmagadd, mpmagsub, crtpre, crtin, crtout, crtprefree, crtresfree \- extended precision arithmetic
+mpsetminbits, mpnew, mpfree, mpbits, mpnorm, mpcopy, mpassign, mprand, mpnrand, strtomp, mpfmt,mptoa, betomp, mptobe, mptober, letomp, mptole, mptolel, mptoui, uitomp, mptoi, itomp, uvtomp, mptouv, vtomp, mptov, mpdigdiv, mpadd, mpsub, mpleft, mpright, mpmul, mpexp, mpmod, mpdiv, mpcmp, mpextendedgcd, mpinvert, mpsignif, mplowbits0, mpvecdigmuladd, mpvecdigmulsub, mpvecadd, mpvecsub, mpveccmp, mpvecmul, mpmagcmp, mpmagadd, mpmagsub, crtpre, crtin, crtout, crtprefree, crtresfree \- extended precision arithmetic
 .SH SYNOPSIS
 .B #include <u.h>
 .br
@@ -34,6 +34,9 @@
 mpint*	mprand(int bits, void (*gen)(uchar*, int), mpint *b)
 .PP
 .B
+mpint*	mpnrand(mpint *n, void (*gen)(uchar*, int), mpint *b)
+.PP
+.B
 mpint*	strtomp(char *buf, char **rptr, int base, mpint *b)
 .PP
 .B
@@ -305,6 +308,14 @@
 .I Gen
 takes a pointer to a string of uchar's and the number
 to fill in.
+.PP
+.I Mpnrand
+uses
+.I gen
+to generate a uniform random number
+.IR x ,
+.if t 0 ≤ \fIx\fR < \fIn\fR.
+.if n 0 ≤ x < n.
 .PP
 .I Strtomp
 and
diff -Nru /n/sources/plan9/sys/src/ape/lib/mp/port/mkfile /sys/src/ape/lib/mp/port/mkfile
--- /n/sources/plan9/sys/src/ape/lib/mp/port/mkfile	Wed Jun 26 23:42:10 2024
+++ /sys/src/ape/lib/mp/port/mkfile	Thu Jun 27 00:04:08 2024
@@ -31,6 +31,7 @@
 	mpextendedgcd\
 	mpinvert\
 	mprand\
+	mpnrand\
 	crt\
 	mptoi\
 	mptoui\
diff -Nru /n/sources/plan9/sys/src/libmp/port/mkfile /sys/src/libmp/port/mkfile
--- /n/sources/plan9/sys/src/libmp/port/mkfile	Wed Jun 26 23:40:10 2024
+++ /sys/src/libmp/port/mkfile	Wed Jun 26 23:59:55 2024
@@ -29,6 +29,7 @@
 	mpextendedgcd\
 	mpinvert\
 	mprand\
+	mpnrand\
 	crt\
 	mptoi\
 	mptoui\
diff -Nru /n/sources/plan9/sys/src/libmp/port/mpnrand.c /sys/src/libmp/port/mpnrand.c
--- /n/sources/plan9/sys/src/libmp/port/mpnrand.c	Wed Dec 31 19:00:00 1969
+++ /sys/src/libmp/port/mpnrand.c	Wed Jun 26 23:59:58 2024
@@ -0,0 +1,24 @@
+#include "os.h"
+#include <mp.h>
+#include <libsec.h>
+#include "dat.h"
+
+/* return uniform random [0..n-1] */
+mpint*
+mpnrand(mpint *n, void (*gen)(uchar*, int), mpint *b)
+{
+	int bits;
+
+	bits = mpsignif(n);
+	if(bits == 0)
+		abort();
+	if(b == nil){
+		b = mpnew(bits);
+		setmalloctag(b, getcallerpc(&n));
+	}
+	do {
+		mprand(bits, gen, b);
+	} while(mpmagcmp(b, n) >= 0);
+
+	return b;
+}