organise

9 files changed, 227 insertions, 0 deletions

diff --git a/3/6_control/20_op_bias.c b/3/6_control/20_op_bias.c
new file mode 100644
index 0000000..b071eb9
--- /dev/null
+++ b/3/6_control/20_op_bias.c
@@ -0,0 +1,10 @@
+#define OP <
+
+// x <- %rdi
+// %rbx <- 15 + (x), bias to round towards zero
+// ZF, SF <- %rdi & %rdi, check if pos or neg
+// %rbx <- x if x >= 0, set to unbiased if pos
+// %rbx <- %rbx >> 4, divide by 16
+short arith(short x) {
+    return x / 16;
+}
diff --git a/3/6_control/21_test_cmov.c b/3/6_control/21_test_cmov.c
new file mode 100644
index 0000000..a90d178
--- /dev/null
+++ b/3/6_control/21_test_cmov.c
@@ -0,0 +1,20 @@
+#include <stdio.h>
+
+// Remember that jumps flip conditionals
+// Also testq rdi rdi and jge test if the sign bit is set
+short test(short x, short y) {
+    short val = 12 + y;
+    if (x < 0) {
+        if (x >= y)
+            val = x | y;
+        else
+            val = x * y;
+    } else if (y >= 10) {
+        val = x / y;
+    }
+    return val;
+}
+
+int main(void) {
+    return 0;
+}
diff --git a/3/6_control/22_loop.c b/3/6_control/22_loop.c
new file mode 100644
index 0000000..73c7710
--- /dev/null
+++ b/3/6_control/22_loop.c
@@ -0,0 +1,51 @@
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+// do
+//    body
+//    while (test);
+//
+// loop:
+//   body
+//   t = test;
+//   if (t)
+//      goto loop;
+
+typedef int64_t fact_t;
+
+long fact_do(long n)
+{
+    long result = 1;
+    do {
+        result *= n;
+        n = n-1;
+    } while (n > 1);
+    return result;
+}
+
+int tmult_ok(fact_t x, fact_t y)
+{
+    fact_t p = x*y;
+    return !x || p/x == y;
+}
+
+fact_t fact_do_int(size_t n)
+{
+    fact_t result = 1;
+    do {
+        if (tmult_ok(result, n)) {
+            result *= n;
+            n = n-1;
+        } else {
+            printf("would overflow this iter, n=%ld\n", n);
+            n = 0;
+        }
+    } while (n > 1);
+    return result;
+}
+
+int main(void) {
+    size_t f = 20;
+    printf("result: %ld, max: %ld, less: %d", fact_do_int(f), INT64_MAX, fact_do_int(f) < INT64_MAX);
+    return 0;
+}
diff --git a/3/6_control/23_reverse_engineer_loop.c b/3/6_control/23_reverse_engineer_loop.c
new file mode 100644
index 0000000..922b317
--- /dev/null
+++ b/3/6_control/23_reverse_engineer_loop.c
@@ -0,0 +1,28 @@
+short dw_loop(short x)
+{
+    short y = x/9;
+    short *p = &x;
+    short n = 4*x;
+    do {
+        x += y;
+        (*p) += 5;
+        n += 2;
+    } while (n > 0);
+    return x;
+}
+
+// x in %rdi
+// dw_loop:
+//    movq %rdi, %rdx           # %rbx <- x
+//    movq %rdi, %rcx           # %rcx <- x
+//    idivq $9, %rcx            # %rcx (y) <- x / 9
+//    leaq (,%rdi,4), %rdx      # %rdx (n) <- x * 4
+// .L2:
+//    leaq 5(%rbx,%rcx), %rcx   # %rbx (x) <- 5 + %rbx (x) + %rcx (y)
+//    subq $1, %rdx             # %rdx (n) <- n - 1
+//    testq %rdx, %rdx          # n > 0 ?
+//    jg .L2                    # if n > 0, goto .L2
+//    rep; ret
+//
+//    A. x in rbx, y in rcx, n in rdx
+//    B. The pointer is never used besides incrementing the value at the address. So it is replaced by a incrementing instruction in the loop.
diff --git a/3/6_control/24_while_loop.c b/3/6_control/24_while_loop.c
new file mode 100644
index 0000000..a3367fc
--- /dev/null
+++ b/3/6_control/24_while_loop.c
@@ -0,0 +1,24 @@
+// while (test)
+//   body
+//
+//  goto test;
+//  loop:
+//      body;
+//  test:
+//      t = test;
+//      if (t)
+//          goto loop;
+
+short loop_while(short a, short b)
+{
+    short result = ;
+    while () {
+        result = ;
+        a = ;
+    }
+    return result;
+}
+
+int main(void) {
+    return 0;
+}
diff --git a/3/6_control/absdiff_goto.c b/3/6_control/absdiff_goto.c
new file mode 100644
index 0000000..dfcb3be
--- /dev/null
+++ b/3/6_control/absdiff_goto.c
@@ -0,0 +1,39 @@
+#include <stdio.h>
+
+// if (!t)
+//    goto false;
+// then-
+// goto done;
+// false:
+//   else-
+//   goto done;
+// done:
+//   ...
+long gotodiff_se(long x, long y)
+{
+    long result;
+    if (x >= y)
+        goto x_ge_y;
+    lt_cnt++;
+    result = y - x;
+    return result;
+
+x_get_y:
+    ge_cnt++;
+    result = x - y;
+    return result;
+}
+
+long gotodiff_se_alternate(long x, long y)
+{
+    long result;
+    if (x < y)
+        goto x_le_y;
+    ge_cnt++;
+    result = x - y;
+    return result;
+x_le_y:
+    lt_cnt++;
+    result = y - x;
+    return result;
+}
diff --git a/3/6_control/comp.c b/3/6_control/comp.c
new file mode 100644
index 0000000..beba875
--- /dev/null
+++ b/3/6_control/comp.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+
+typedef char data_t;
+
+#define COMP <=
+
+// a in rdx, b in rsi
+//
+// cmpl %esi, %edi  (Compare long (double word, or 4 bytes). (a - b) )
+// setl %al (set lower? %rax return value)
+//
+// COMP is <, and data_t is 32 bits so maybe int or unsigned int or float
+//
+// cmpw %si, %di (Compare word (a-b), short)
+// setge %al     (Greater than or equal >=)
+//
+// cmpb %sil, %dil (Compare byte (a-b))
+// setbe %al (Comp <=)
+//
+// cmpq %rsi, %rdi (Compare 8 bytes quad words (long , double, char *))
+// setne %al
+int comp(data_t a, data_t b) {
+    return a COMP b;
+}
+
+#define TEST >
+
+int test(data_t a) {
+    return a TEST 0;
+}
+
+int main() {
+    printf("%x hello world", comp(1, 2));
+    return 0;
+}
+
diff --git a/3/6_control/cond.c b/3/6_control/cond.c
new file mode 100644
index 0000000..8b647bf
--- /dev/null
+++ b/3/6_control/cond.c
@@ -0,0 +1,6 @@
+void cond(short a, short *p)
+{
+    if (a && *p < a) {
+        *p = a;
+    }
+}
diff --git a/3/6_control/missing.c b/3/6_control/missing.c
new file mode 100644
index 0000000..1b8067b
--- /dev/null
+++ b/3/6_control/missing.c
@@ -0,0 +1,13 @@
+short test(short x, short y, short z) {
+    short val = (z+y) - x;
+    if (z > 5) {
+        if (y > 2) {
+            val = x/z;
+        } else {
+            val = x/y;
+        }
+    } else if (z < 3) {
+        val = z/y;
+    }
+    return val;
+}