random seed initialization added, tweaked sequence generation

c64/basic/math/e0be.rnd_generate.s

@@ -3,7 +3,7 @@
 // #LAYOUT# *   *       #IGNORE
 
 //
-// A fast random generator, idea from:
+// A fast pseudorandom generator, modified idea from:
 // - https://codebase64.org/doku.php?id=base:32bit_galois_lfsr
 //
 // Output:
@@ -15,8 +15,6 @@
 
 rnd_generate:
 
-	// Generate new 4-byte random number
-
 	asl RNDX+1
 	rol RNDX+2
 	rol RNDX+3
@@ -27,12 +25,15 @@ rnd_generate:
 	lda RNDX+1
 	eor #$B7
 	sta RNDX+1
+
 	lda RNDX+2
 	eor #$1D
 	sta RNDX+2
+
 	lda RNDX+3
 	eor #$C1
 	sta RNDX+3
+
 	lda RNDX+4
 	eor #$04
 	sta RNDX+4
@@ -41,23 +42,32 @@ rnd_generate:
 
 rnd_generate_copy:
 
-	// Copy the number to FAC1, order changed on purpose
+	// Copy the generated number to FAC1, mangle it a little
 
 	lda RNDX+3
+	eor #$62
 	sta FAC1_mantissa+0
+
 	lda RNDX+1
+	eor #$4E
 	sta FAC1_mantissa+1
-	lda RNDX+2
-	sta FAC1_mantissa+2
+
 	lda RNDX+4
+	eor #$97
+	sta FAC1_mantissa+2
+
+	lda RNDX+2
 	sta FAC1_mantissa+3
-	
+
+	// FALLTROUGH
+
+rnd_generate_finalize:
+
 	lda #$00
-	sta FACOV
 	sta FAC1_sign
 	
 	lda #$80
+	sta FACOV                          // just to prevent 0 after normalization
 	sta FAC1_exponent
-	sta RNDX+0                         // in case someone tries to use the float directly
 	
 	jmp normal_FAC1