util: New function udiv64(): 64/32 -> 32q

inc/util.h

@@ -69,6 +69,8 @@ int snprintf(char *str, size_t size, const char *format, ...)
 #define htobe16(x) _rev16(x)
 #define htobe32(x) _rev32(x)
 
+uint32_t udiv64(uint64_t dividend, uint32_t divisor);
+
 /* Arena-based memory allocation */
 void *arena_alloc(uint32_t sz);
 uint32_t arena_total(void);

src/util.c

@@ -335,6 +335,18 @@ unsigned int popcount(uint32_t x)
     return (((x + (x >> 4)) & 0x0f0f0f0f) * 0x01010101) >> 24;
 }
 
+
+/* 64:32->32q division requiring 32:32->64 multiply. Cortex M3+ */
+uint32_t udiv64(uint64_t dividend, uint32_t divisor)
+{
+    uint32_t x, q = 0;
+    for (x = 1u<<31; x != 0; x >>= 1) {
+        if (((uint64_t)(q|x)*divisor) <= dividend)
+            q |= x;
+    }
+    return q;
+}
+
 /*
  * Local variables:
  * mode: C