From 5bd0a65aaa5345edfb6a1795a38d0c328da8f35d Mon Sep 17 00:00:00 2001
From: haskal <haskal@awoo.systems>
Date: Thu, 21 Jan 2021 18:07:59 -0500
Subject: [PATCH] float -> bits without casting

---
 ieee754/float.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 ieee754/float.c

diff --git a/ieee754/float.c b/ieee754/float.c
new file mode 100644
index 0000000..e04e72b
--- /dev/null
+++ b/ieee754/float.c
@@ -0,0 +1,96 @@
+#include <stdio.h>
+#include <math.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+uint32_t getbits(float f) {
+    union { float f; uint32_t u; } hax;
+    hax.f = f;
+    return hax.u;
+}
+
+void printb(uint32_t u) {
+    for (uint32_t i = 32; i > 0; i--) {
+        if (i == 31 || i == 23) {
+            printf(" ");
+        }
+        printf("%d", (u >> (i - 1))&1);
+    }
+    printf("\n");
+}
+
+uint32_t getbits_meow(float f) {
+    printf("original:                  ");
+    printb(getbits(f));
+
+    // these are untested lol
+    if (f == 0.0f) {
+        return 0;
+    } else if (f == -0.0f) {
+        return 1 << 31;
+    } else if (f == NAN) {
+        // not always accurate
+        // there are multiple kinds of nan
+        // idk if there's much we can do tbh
+        return 0xFFFFFFFF;
+    } else if (f == INFINITY) {
+        return 0x7F800000;
+    } else if (f == -INFINITY) {
+        return 0xFF800000;
+    }
+    uint32_t sign = 0;
+    if (f < 0) {
+        sign = 1;
+        f = -f;
+    }
+
+    uint32_t div_count = 0;
+    volatile float f2 = f;
+    while (true) {
+        volatile float f3 = f2 / 2.0f;
+        volatile float f4 = f3 * 2.0f;
+        if (f4 != f2) {
+            break;
+        }
+        div_count++;
+        f2 = f3;
+    }
+
+    uint32_t mul_count = 0;
+    f2 = f;
+    while (true) {
+        volatile float f3 = f2 * 2.0f;
+        volatile float f4 = f3 / 2.0f;
+        if (f4 != f2) {
+            break;
+        }
+        mul_count++;
+        f2 = f3;
+    }
+
+    // TODO : subnormal numbers (div_count == 0 ?)
+
+    // the div count is cool and all but it allows going into subnormal range while maintaing
+    // equality which is not good
+    // so we use the mul count
+    uint32_t exp = 0xFE - mul_count;
+
+    for (uint32_t i = 0; i < 254-127-23; i++) {
+        f2 = f2 / 2.0f;
+    }
+
+    uint32_t mantissa = ((uint32_t) f2) & 0b11111111111111111111111;
+
+    printf("result:                    ");
+    printb((sign << 31) | ((exp & 0xFF) << 23) | mantissa);
+
+    printf("----------------\n");
+}
+
+int main() {
+    getbits_meow(0.00000002f);
+    getbits_meow(0.001f);
+    getbits_meow(10.0f);
+    getbits_meow(100000.0f);
+    getbits_meow(10000000000.0f);
+}