boot2

commit 445f751aceb58da4012431734742011229962bea
parent 3c1ff085bd23764d9ade055decf074f17d7761e0
Author: Ryan Sepassi <rsepassi@gmail.com>
Date:   Mon, 27 Apr 2026 09:47:01 -0700

cc/util: round buf caps to powers of two

bv_capacity_for now returns the smallest pow2 >= n (was > n), so
asking for 2^k bytes lands a 2^k buffer instead of 2^(k+1). Drop the
"-1" workaround; constants are exact powers of two.

Diffstat:
M
cc/util.scm
 | 
20
+++++++++-----------

1 file changed, 9 insertions(+), 11 deletions(-)
diff --git a/cc/util.scm b/cc/util.scm
@@ -126,17 +126,15 @@
 ;; 64 MiB heap. Bump these when a workload overflows; the buf-overflow
 ;; die() reports off/len/cap so misses are easy to diagnose.
 ;;
-;; Each cap is one less than a power of two: scheme1's bv_capacity_for
-;; rounds the requested length up to the smallest power of two STRICTLY
-;; GREATER than it, so asking for 2^k bytes actually consumes 2^(k+1)
-;; of heap. Using 2^k - 1 gives the next-pow2 step EQUAL to 2^k, which
-;; is the storage we actually intended.
-(define %BUF-CAP-TEXT     8388607)   ; ≈8 MiB:   .text + entry stub
-(define %BUF-CAP-DATA     2097151)   ; ≈2 MiB:   .data (strings, globals)
-(define %BUF-CAP-BSS      2097151)   ; ≈2 MiB:   .bss
-(define %BUF-CAP-FN       262143)    ; ≈256 KiB: per-fn body asm
-(define %BUF-CAP-PROLOGUE 16383)     ; ≈16 KiB:  per-fn prologue
-(define %BUF-CAP-DEFAULT  65535)     ; ≈64 KiB:  make-buf fallback
+;; Each cap is a power of two. scheme1's bv_capacity_for rounds the
+;; requested length up to the smallest power of two ≥ n, so asking for
+;; 2^k bytes consumes exactly 2^k of heap.
+(define %BUF-CAP-TEXT     8388608)   ; 8 MiB:   .text + entry stub
+(define %BUF-CAP-DATA     2097152)   ; 2 MiB:   .data (strings, globals)
+(define %BUF-CAP-BSS      2097152)   ; 2 MiB:   .bss
+(define %BUF-CAP-FN       262144)    ; 256 KiB: per-fn body asm
+(define %BUF-CAP-PROLOGUE 16384)     ; 16 KiB:  per-fn prologue
+(define %BUF-CAP-DEFAULT  65536)     ; 64 KiB:  make-buf fallback
 
 (define-record-type buf
   (%buf storage offset cap)