bootstrap 08: use shift instead of rot

1 files changed, 19 insertions, 13 deletions

diff --git a/content/bootstrapGcc/08_tcc_and_mescc.md b/content/bootstrapGcc/08_tcc_and_mescc.md
index 43666fb..3c18a39 100644
--- a/content/bootstrapGcc/08_tcc_and_mescc.md
+++ b/content/bootstrapGcc/08_tcc_and_mescc.md
@@ -45,7 +45,7 @@ This is going to be veery long post, so take a ToC to help you out:
     7. [Bootstrappable TinyCC's `long double` support was missing](#long-double)
     8. [MesCC struct initialization issues](#mescc-struct-init)
     9. [MesCC vs TinyCC size problems](#size-problems)
-    10. [MesCC add support for signed rotation](#mes-signed-rotation)
+    10. [MesCC add support for signed shift operation](#mes-signed-shift)
     11. [MesCC switch/case falls-back to default case](#broken-case)
     12. [Boostrappable TinyCC problems with GOT](#got)
     13. [Bootstrappable TinyCC generates wrong assembly in conditionals](#wrong-conditionals)
@@ -433,10 +433,10 @@ wide. You can see this happening in `riscv64-gen.c`, for example, here:
     EI(0x13, 0, rr, rr, (int)pi << 20 >> 20);   // addi RR, RR, lo(up(fc))
 ```
 
-The rotation there is done to clear the upper 20 bits of the pi variable. This
-code's behavior might be different from one platform to another. Taking the
-example before, of that possible platform that only has 8 bit integers, this
-code would send a `0` instead of the lower 12 bits of `pi`.
+The bit shifting there is done to clear the upper 20 bits of the pi variable.
+This code's behavior might be different from one platform to another. Taking
+the example before, of that possible platform that only has 8 bit integers,
+this code would send a `0` instead of the lower 12 bits of `pi`.
 
 In our case, we had MesCC using the whole register width, 64bits, for temporary
 values so the lowest `44` bits were left and the next assertion that checked
@@ -461,18 +461,18 @@ we all became paranoids about integers and we still think some extra errors
 will arise from them in the future. Integers are hard.
 
 
-#### MesCC add support for signed rotation {#mes-signed-rotation}
+#### MesCC add support for signed shifting {#mes-signed-shift}
 
 Integers were in our minds for long, as described in the previous block, but I
 didn't talk about signedness in that one.
 
 Following one of the crazy errors we had in TinyCC, I somehow realized (I don't
-remember how!) that we were missing signed rotation support in MesCC. I think
+remember how!) that we were missing signed shifting support in MesCC. I think
 that I found this while doing some research of the code MesCC was outputting
-when I spotted some rotations done using unsigned instructions for signed
+when I spotted some bit shifts done using unsigned instructions for signed
 values and I started digging in MesCC to find out why. I finally realized that
-there was no support for that and the rotation operation wasn't selected
-depending on the signedness of the value being rotated.
+there was no support for that and the shift operation wasn't selected
+depending on the signedness of the value being shifted.
 
 Let's see this with an example:
 
@@ -487,17 +487,23 @@ a >> 4;
 b >> 4;
 ```
 
-In the example you can see the rotation operation does not work the same way if
+In the example you can see the shifting operation does not work the same way if
 the value is signed or not. If you always use the unsigned version of the `>>`
 operation, you don't have the results you expected. Signs are also hard.
 
 In this case, like in many others, the fix was easier than realizing what was
-going wrong. I just added support for the signed rotation operation, not only
+going wrong. I just added support for the signed shifting operation, not only
 for RISC-V but for all architectures, and I added the correct signedness check
-to the rotation operation to select the correct instruction. The patch (see
+to the shifting operation to select the correct instruction. The patch (see
 [88f24ea8][signed-rotation] in Mes) is very clean and easy to read, because
 MesCC's codebase is really well ordered.
 
+> EDIT: Some person in the web noted I called the *bit-shift* operations
+> *rotation* operations. I normally use both words interchangeably but it is
+> true they don't mean the exact same thing. A shift is when the values are
+> lost, and a rotation when they come from the other side of the register. I
+> edited the article to use the correct word.
+
 [signed-rotation]: https://github.com/ekaitz-zarraga/mes/commit/88f24ea8661dd279c2a919f8fbd5f601bb2509ae