Data lab initialization

1 files changed, 151 insertions, 0 deletions

diff --git a/datalab-handout/fshow.c b/datalab-handout/fshow.c
new file mode 100644
index 0000000..fc918f6
--- /dev/null
+++ b/datalab-handout/fshow.c
@@ -0,0 +1,151 @@
+/* Display structure of floating-point numbers */
+
+#include <stdio.h>
+#include <stdlib.h>
+float strtof(const char *nptr, char **endptr);
+
+#define FLOAT_SIZE 32
+#define FRAC_SIZE 23
+#define EXP_SIZE 8
+#define BIAS ((1<<(EXP_SIZE-1))-1)
+#define FRAC_MASK ((1<<FRAC_SIZE)-1)
+#define EXP_MASK ((1<<EXP_SIZE)-1)
+
+/* Floating point helpers */
+unsigned f2u(float f)
+{
+  union {
+    unsigned u;
+    float f;
+  } v;
+  v.u = 0;
+  v.f = f;
+  return v.u;
+}
+
+static float u2f(unsigned u)
+{
+  union {
+    unsigned u;
+    float f;
+  } v;
+  v.u = u;
+  return v.f;
+}
+
+/* Get exponent */
+unsigned get_exp(unsigned uf)
+{
+  return (uf>>FRAC_SIZE) & EXP_MASK;
+}
+
+/* Get fraction */
+unsigned get_frac(unsigned uf)
+{
+  return uf & FRAC_MASK;
+}
+
+/* Get sign */
+unsigned get_sign(unsigned uf)
+{
+  return (uf>>(FLOAT_SIZE-1)) & 0x1;
+}
+
+void show_float(unsigned uf)
+{
+  float f = u2f(uf);
+  unsigned exp = get_exp(uf);
+  unsigned frac = get_frac(uf);
+  unsigned sign = get_sign(uf);
+
+  printf("\nFloating point value %.10g\n", f);
+  printf("Bit Representation 0x%.8x, sign = %x, exponent = 0x%.2x, fraction = 0x%.6x\n",
+	 uf, sign, exp, frac);
+  if (exp == EXP_MASK) {
+    if (frac == 0) {
+      printf("%cInfinity\n", sign ? '-' : '+');
+    } else
+      printf("Not-A-Number\n");
+  } else {
+    int denorm = (exp == 0);
+    int uexp = denorm ? 1-BIAS : exp - BIAS;
+    int mantissa = denorm ? frac : frac + (1<<FRAC_SIZE);
+    float fman = (float) mantissa / (float) (1<<FRAC_SIZE);
+    printf("%s.  %c%.10f X 2^(%d)\n",
+	   denorm ? "Denormalized" : "Normalized",
+	   sign ? '-' : '+',
+	   fman, uexp);
+  }
+}
+
+/* Extract hex/decimal/or float value from string */
+static int get_num_val(char *sval, unsigned *valp) {
+  char *endp;
+  /* See if it's an integer or floating point */
+  int ishex = 0;
+  int isfloat = 0;
+  int i;
+  for (i = 0; sval[i]; i++) {
+    switch (sval[i]) {
+    case 'x':
+    case 'X':
+      ishex = 1;
+      break;
+    case 'e':
+    case 'E':
+      if (!ishex)
+	isfloat = 1;
+      break;
+    case '.':
+      isfloat = 1;
+      break;
+    default:
+      break;
+    }
+  }
+  if (isfloat) {
+    float fval = strtof(sval, &endp);
+    if (!*endp) {
+      *valp = *(unsigned *) &fval;
+      return 1;
+    }
+    return 0;
+  } else {
+    long long int llval = strtoll(sval, &endp, 0);
+    long long int upperbits = llval >> 31;
+    /* will give -1 for negative, 0 or 1 for positive */
+    if (valp && (upperbits == 0 || upperbits == -1 || upperbits == 1)) {
+      *valp = (unsigned) llval;
+      return 1;
+    }
+    return 0;
+  }
+}
+
+
+void usage(char *fname) {
+  printf("Usage: %s val1 val2 ...\n", fname);
+  printf("Values may be given as hex patterns or as floating point numbers\n");
+  exit(0);
+}
+
+
+int main(int argc, char *argv[])
+{
+  int i;
+  unsigned uf;
+  if (argc < 2)
+    usage(argv[0]);
+  for (i = 1; i < argc; i++) {
+    char *sval = argv[i];
+    if (get_num_val(sval, &uf)) {
+      show_float(uf);
+    } else {
+      printf("Invalid 32-bit number: '%s'\n", sval);
+      usage(argv[0]);
+    }
+  }
+  return 0;
+}
+
+