Added an implementation of Lehmer random number generator with Lecuyer constant,...

[xonotic/darkplaces.git] / mathlib.c

diff --git a/mathlib.c b/mathlib.c
index 738965a0491b5beb305f4cf7c6dc64189b11cacb..b228576803c9f1956fa03040b0eec9e61f651b97 100644 (file)
--- a/mathlib.c
+++ b/mathlib.c
@@ -900,3 +900,82 @@ int LoopingFrameNumberFromDouble(double t, int loopframes)
                return (int)t;
 }
 
+static unsigned int mul_Lecuyer[4] = { 0x12e15e35, 0xb500f16e, 0x2e714eb2, 0xb37916a5 };
+
+static void mul128(unsigned int a[], unsigned int b[], unsigned int dest[4])
+{
+       unsigned long long t[4];
+       t[0] = a[0] * b[0];
+       t[1] = a[1] * b[1];
+       t[2] = a[2] * b[2];
+       t[3] = a[3] * b[3];
+
+       // this is complicated because C doesn't have a way to make use of the
+       // cpu status carry flag, so we do it all in reverse order from what
+       // would otherwise make sense, and have to make multiple passes...
+       t[3] += t[2] >> 32; t[2] &= 0xffffffff;
+       t[2] += t[1] >> 32; t[1] &= 0xffffffff;
+       t[1] += t[0] >> 32; t[0] &= 0xffffffff;
+
+       t[3] += t[2] >> 32; t[2] &= 0xffffffff;
+       t[2] += t[1] >> 32; t[1] &= 0xffffffff;
+
+       t[3] += t[2] >> 32; t[2] &= 0xffffffff;
+
+       dest[0] = t[0] & 0xffffffff;
+       dest[1] = t[1] & 0xffffffff;
+       dest[2] = t[2] & 0xffffffff;
+       dest[3] = t[3] & 0xffffffff;
+}
+
+void Math_RandomSeed_Reset(randomseed_t *r)
+{
+       r->s[0] = 1;
+       r->s[1] = 0;
+       r->s[2] = 0;
+       r->s[3] = 0;
+}
+
+void Math_RandomSeed_FromInt(randomseed_t *r, unsigned int n)
+{
+       // if the entire s[] is zero the algorithm would break completely, so make sure it isn't zero by putting a 1 here
+       r->s[0] = 1;
+       r->s[1] = 0;
+       r->s[2] = 0;
+       r->s[3] = n;
+}
+
+unsigned long long Math_rand64(randomseed_t *r)
+{
+       unsigned int o[4];
+       mul128(r->s, mul_Lecuyer, o);
+       r->s[0] = o[0];
+       r->s[1] = o[1];
+       r->s[2] = o[2];
+       r->s[3] = o[3];
+       return ((unsigned long long)o[3] << 32) + o[2];
+}
+
+float Math_randomf(randomseed_t *r)
+{
+       unsigned long long n = Math_rand64(r);
+       return n * (0.25f / 0x80000000 / 0x80000000);
+}
+
+float Math_crandomf(randomseed_t *r)
+{
+       // do this with a signed number and double the result, so we make use of all parts of the cow
+       long long n = (long long)Math_rand64(r);
+       return n * (0.5f / 0x80000000 / 0x80000000);
+}
+
+float Math_randomrangef(randomseed_t *r, float minf, float maxf)
+{
+       return Math_randomf(r) * (maxf - minf) + minf;
+}
+
+int Math_randomrangei(randomseed_t *r, int mini, int maxi)
+{
+       unsigned long long n = Math_rand64(r);
+       return (int)(((n >> 33) * (maxi - mini) + mini) >> 31);
+}