Don't cast signed to unsigned before shifting

Unfortunately, signed->unsigned casts do not commute with shifts.  We
take care to only extend the range when it needs extending, now.  This
was previously causing issues with subborrow.

We should really get proofs about casts in C semantics at some point
soon.

Fixes #489

1 files changed, 14 insertions, 12 deletions

diff --git a/p384_32.c b/p384_32.c
index 113c1db4a..95b6c73d3 100644
--- a/p384_32.c
+++ b/p384_32.c
@@ -14,6 +14,8 @@
 #include <stdint.h>
 typedef unsigned char fiat_p384_uint1;
 typedef signed char fiat_p384_int1;
+typedef signed __int128 fiat_p384_int128;
+typedef unsigned __int128 fiat_p384_uint128;
 
 
 /*
@@ -44,7 +46,7 @@ static void fiat_p384_addcarryx_u32(uint32_t* out1, fiat_p384_uint1* out2, fiat_
  */
 static void fiat_p384_subborrowx_u32(uint32_t* out1, fiat_p384_uint1* out2, fiat_p384_uint1 arg1, uint32_t arg2, uint32_t arg3) {
   int64_t x1 = ((arg2 - (int64_t)arg1) - arg3);
-  fiat_p384_int1 x2 = (fiat_p384_int1)((uint64_t)x1 >> 32);
+  fiat_p384_int1 x2 = (fiat_p384_int1)((fiat_p384_int128)x1 >> 32);
   uint32_t x3 = (uint32_t)(x1 & UINT32_C(0xffffffff));
   *out1 = x3;
   *out2 = (fiat_p384_uint1)(0x0 - x2);
@@ -7300,7 +7302,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x16 = (uint8_t)(x13 & UINT8_C(0xff));
   uint8_t x17 = (uint8_t)(x15 >> 8);
   uint8_t x18 = (uint8_t)(x15 & UINT8_C(0xff));
-  fiat_p384_uint1 x19 = (fiat_p384_uint1)(x17 >> 8);
+  fiat_p384_uint1 x19 = (fiat_p384_uint1)((int64_t)x17 >> 8);
   uint8_t x20 = (uint8_t)(x17 & UINT8_C(0xff));
   uint32_t x21 = (x19 + x11);
   uint32_t x22 = (x21 >> 8);
@@ -7309,7 +7311,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x25 = (uint8_t)(x22 & UINT8_C(0xff));
   uint8_t x26 = (uint8_t)(x24 >> 8);
   uint8_t x27 = (uint8_t)(x24 & UINT8_C(0xff));
-  fiat_p384_uint1 x28 = (fiat_p384_uint1)(x26 >> 8);
+  fiat_p384_uint1 x28 = (fiat_p384_uint1)((int64_t)x26 >> 8);
   uint8_t x29 = (uint8_t)(x26 & UINT8_C(0xff));
   uint32_t x30 = (x28 + x10);
   uint32_t x31 = (x30 >> 8);
@@ -7318,7 +7320,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x34 = (uint8_t)(x31 & UINT8_C(0xff));
   uint8_t x35 = (uint8_t)(x33 >> 8);
   uint8_t x36 = (uint8_t)(x33 & UINT8_C(0xff));
-  fiat_p384_uint1 x37 = (fiat_p384_uint1)(x35 >> 8);
+  fiat_p384_uint1 x37 = (fiat_p384_uint1)((int64_t)x35 >> 8);
   uint8_t x38 = (uint8_t)(x35 & UINT8_C(0xff));
   uint32_t x39 = (x37 + x9);
   uint32_t x40 = (x39 >> 8);
@@ -7327,7 +7329,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x43 = (uint8_t)(x40 & UINT8_C(0xff));
   uint8_t x44 = (uint8_t)(x42 >> 8);
   uint8_t x45 = (uint8_t)(x42 & UINT8_C(0xff));
-  fiat_p384_uint1 x46 = (fiat_p384_uint1)(x44 >> 8);
+  fiat_p384_uint1 x46 = (fiat_p384_uint1)((int64_t)x44 >> 8);
   uint8_t x47 = (uint8_t)(x44 & UINT8_C(0xff));
   uint32_t x48 = (x46 + x8);
   uint32_t x49 = (x48 >> 8);
@@ -7336,7 +7338,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x52 = (uint8_t)(x49 & UINT8_C(0xff));
   uint8_t x53 = (uint8_t)(x51 >> 8);
   uint8_t x54 = (uint8_t)(x51 & UINT8_C(0xff));
-  fiat_p384_uint1 x55 = (fiat_p384_uint1)(x53 >> 8);
+  fiat_p384_uint1 x55 = (fiat_p384_uint1)((int64_t)x53 >> 8);
   uint8_t x56 = (uint8_t)(x53 & UINT8_C(0xff));
   uint32_t x57 = (x55 + x7);
   uint32_t x58 = (x57 >> 8);
@@ -7345,7 +7347,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x61 = (uint8_t)(x58 & UINT8_C(0xff));
   uint8_t x62 = (uint8_t)(x60 >> 8);
   uint8_t x63 = (uint8_t)(x60 & UINT8_C(0xff));
-  fiat_p384_uint1 x64 = (fiat_p384_uint1)(x62 >> 8);
+  fiat_p384_uint1 x64 = (fiat_p384_uint1)((int64_t)x62 >> 8);
   uint8_t x65 = (uint8_t)(x62 & UINT8_C(0xff));
   uint32_t x66 = (x64 + x6);
   uint32_t x67 = (x66 >> 8);
@@ -7354,7 +7356,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x70 = (uint8_t)(x67 & UINT8_C(0xff));
   uint8_t x71 = (uint8_t)(x69 >> 8);
   uint8_t x72 = (uint8_t)(x69 & UINT8_C(0xff));
-  fiat_p384_uint1 x73 = (fiat_p384_uint1)(x71 >> 8);
+  fiat_p384_uint1 x73 = (fiat_p384_uint1)((int64_t)x71 >> 8);
   uint8_t x74 = (uint8_t)(x71 & UINT8_C(0xff));
   uint32_t x75 = (x73 + x5);
   uint32_t x76 = (x75 >> 8);
@@ -7363,7 +7365,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x79 = (uint8_t)(x76 & UINT8_C(0xff));
   uint8_t x80 = (uint8_t)(x78 >> 8);
   uint8_t x81 = (uint8_t)(x78 & UINT8_C(0xff));
-  fiat_p384_uint1 x82 = (fiat_p384_uint1)(x80 >> 8);
+  fiat_p384_uint1 x82 = (fiat_p384_uint1)((int64_t)x80 >> 8);
   uint8_t x83 = (uint8_t)(x80 & UINT8_C(0xff));
   uint32_t x84 = (x82 + x4);
   uint32_t x85 = (x84 >> 8);
@@ -7372,7 +7374,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x88 = (uint8_t)(x85 & UINT8_C(0xff));
   uint8_t x89 = (uint8_t)(x87 >> 8);
   uint8_t x90 = (uint8_t)(x87 & UINT8_C(0xff));
-  fiat_p384_uint1 x91 = (fiat_p384_uint1)(x89 >> 8);
+  fiat_p384_uint1 x91 = (fiat_p384_uint1)((int64_t)x89 >> 8);
   uint8_t x92 = (uint8_t)(x89 & UINT8_C(0xff));
   uint32_t x93 = (x91 + x3);
   uint32_t x94 = (x93 >> 8);
@@ -7381,7 +7383,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x97 = (uint8_t)(x94 & UINT8_C(0xff));
   uint8_t x98 = (uint8_t)(x96 >> 8);
   uint8_t x99 = (uint8_t)(x96 & UINT8_C(0xff));
-  fiat_p384_uint1 x100 = (fiat_p384_uint1)(x98 >> 8);
+  fiat_p384_uint1 x100 = (fiat_p384_uint1)((int64_t)x98 >> 8);
   uint8_t x101 = (uint8_t)(x98 & UINT8_C(0xff));
   uint32_t x102 = (x100 + x2);
   uint32_t x103 = (x102 >> 8);
@@ -7390,7 +7392,7 @@ static void fiat_p384_to_bytes(uint8_t out1[48], const uint32_t arg1[12]) {
   uint8_t x106 = (uint8_t)(x103 & UINT8_C(0xff));
   uint8_t x107 = (uint8_t)(x105 >> 8);
   uint8_t x108 = (uint8_t)(x105 & UINT8_C(0xff));
-  fiat_p384_uint1 x109 = (fiat_p384_uint1)(x107 >> 8);
+  fiat_p384_uint1 x109 = (fiat_p384_uint1)((int64_t)x107 >> 8);
   uint8_t x110 = (uint8_t)(x107 & UINT8_C(0xff));
   uint32_t x111 = (x109 + x1);
   uint32_t x112 = (x111 >> 8);