organise

1 files changed, 112 insertions, 0 deletions

diff --git a/2/homework/2.90.c b/2/homework/2.90.c
new file mode 100644
index 0000000..8eefec3
--- /dev/null
+++ b/2/homework/2.90.c
@@ -0,0 +1,112 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <limits.h>
+#include <math.h>
+#include "../code/data/show-bytes.c"
+
+
+float my_u2f(unsigned int my_u) {
+    assert(sizeof(unsigned int) == sizeof(float));
+    union {
+        unsigned int u;
+        float f;
+    } my_union;
+    /* Apparently you cannot print the bytes of a float directly? like this printf("%x\n", f); */
+    my_union.u = my_u;
+    return my_union.f;
+}
+
+float fpwr2(int x)
+{
+    /* Result exponent and fraction */
+    unsigned exp, frac;
+    unsigned u;
+
+    int k = 8;
+    int n = 23;
+
+    int bias = (1<<(k-1))-1;
+    int max_e = ((1<<k) - 2) - bias;
+
+    if (x < 1-bias-n) {
+        /*  Too small. Return 0.0 */
+        exp = 0;
+        frac = 0;
+    } else if (x < 1-bias) {
+        /* Denormalized, [(1-bias-n), (1-bias)]  [-139, -126] */
+        exp = 0;
+        frac = 1<<(x+1-bias-n);
+    } else if (x<=max_e) {
+        /* Normalized */
+        exp = x+bias;
+        frac = 0;
+    } else {
+        /* Too big. Return +oo */
+        exp = (1<<8)-1;
+        frac = 0;
+    }
+
+    /* Pack exp and frac into 32 bits */
+    u = (exp << 23) | frac;
+    /* Return as float */
+    return my_u2f(u);
+}
+
+
+int main(void) {
+
+    /* 2.90 */
+    printf("%f\n", fpwr2(-1));  /* 65536 */
+    printf("%f\n", fpwr2(16));  /* 65536 */
+    printf("%f\n", fpwr2(15));  /* 32768 */
+    printf("%f\n", fpwr2(14));  /* 16384 */
+    printf("%f\n", fpwr2(13));  /* 8192 */
+    printf("%f\n", fpwr2(12));  /* 4096 */
+    printf("%f\n", fpwr2(11));  /* 2048 */
+    printf("%f\n", fpwr2(10));  /* 1024 */
+    printf("%f\n", fpwr2(128));
+    return 0;
+
+    /* 2.91 */
+    printf("%x\n", 0b01000000010010010000111111011011);
+    /*
+      0 10000000 10010010000111111011011
+      E = 128-127 = 1
+      M = 1 + f
+      f = (2^22+2^19+2^16+2^11+2^10+2^9+2^8+2^7+2^6+2^4+2^3+2^1+2^0)/2^23
+      V = (2^E)(M)
+
+      13176795/4194304
+
+      22/7 = 2(1+f)
+      11/7 = (1+f)
+      4/7 = f
+
+      n = 0.yyy = f
+      n = Y/((1<<k) - 1)
+      n = 4/((1<<3) - 1)
+      0 10000000 [100]+
+    */
+    show_float(22.0f/7.0f);
+    printf("%b\n", 0x40492492);
+    /* so we have 22/7
+       0 10000000 10010010010010010010010
+       and the approx
+       0 10000000 10010010000111111011011
+       at the 9th position the values diverge
+     */
+    return 0;
+
+    /* 2.90 */
+    printf("%f\n", fpwr2(-1));  /* 65536 */
+    printf("%f\n", fpwr2(16));  /* 65536 */
+    printf("%f\n", fpwr2(15));  /* 32768 */
+    printf("%f\n", fpwr2(14));  /* 16384 */
+    printf("%f\n", fpwr2(13));  /* 8192 */
+    printf("%f\n", fpwr2(12));  /* 4096 */
+    printf("%f\n", fpwr2(11));  /* 2048 */
+    printf("%f\n", fpwr2(10));  /* 1024 */
+    printf("%f\n", fpwr2(128));
+    return 0;
+}