Add jrand48()/nrand48() compat functions

These functions are not available on all platforms.

app/meson.build

@@ -170,6 +170,8 @@ check_functions = [
     'strdup',
     'asprintf',
     'vasprintf',
+    'nrand48',
+    'jrand48',
 ]
 
 foreach f : check_functions

app/src/compat.c

@@ -51,3 +51,47 @@ int vasprintf(char **strp, const char *fmt, va_list ap) {
     return len;
 }
 #endif
+
+#if !defined(HAVE_NRAND48) || !defined(HAVE_JRAND48)
+#define SC_RAND48_MASK UINT64_C(0xFFFFFFFFFFFF) // 48 bits
+#define SC_RAND48_A UINT64_C(0x5DEECE66D)
+#define SC_RAND48_C 0xB
+static inline uint64_t rand_iter48(uint64_t x) {
+    assert((x & ~SC_RAND48_MASK) == 0);
+    return (x * SC_RAND48_A + SC_RAND48_C) & SC_RAND48_MASK;
+}
+
+static uint64_t rand_iter48_xsubi(unsigned short xsubi[3]) {
+    uint64_t x = ((uint64_t) xsubi[0] << 32)
+               | ((uint64_t) xsubi[1] << 16)
+               | xsubi[2];
+
+    x = rand_iter48(x);
+
+    xsubi[0] = (x >> 32) & 0XFFFF;
+    xsubi[1] = (x >> 16) & 0XFFFF;
+    xsubi[2] = x & 0XFFFF;
+
+    return x;
+}
+
+#ifndef HAVE_NRAND48
+long nrand48(unsigned short xsubi[3]) {
+    // range [0, 2^31)
+    return rand_iter48_xsubi(xsubi) >> 17;
+}
+#endif
+
+#ifndef HAVE_JRAND48
+long jrand48(unsigned short xsubi[3]) {
+    // range [-2^31, 2^31)
+    union {
+        uint32_t u;
+        int32_t i;
+    } v;
+    v.u = rand_iter48_xsubi(xsubi) >> 16;
+    return v.i;
+}
+#endif
+
+#endif

app/src/compat.h

@@ -59,4 +59,12 @@ int asprintf(char **strp, const char *fmt, ...);
 int vasprintf(char **strp, const char *fmt, va_list ap);
 #endif
 
+#ifndef HAVE_NRAND48
+long nrand48(unsigned short xsubi[3]);
+#endif
+
+#ifndef HAVE_JRAND48
+long jrand48(unsigned short xsubi[3]);
+#endif
+
 #endif